Squeezing through border bottlenecks during peak holidays and rush hours can be time- consuming. Avoid crossing 7–9 a.m. and 4:30–6:30 p.m. If you can manage it, cross instead during late-night or early-morning hours. Furthermore, the U.S. Customs and Border Patrol maintains an informative border crossing page. Visit http://apps.cbp.gov/bwt, and click the “Border Wait Times” link on the right side.

Just before returning across the border with your car, park and have an aduana (customs) official remove and cancel the holographic identity sticker that you received on entry. If possible, get a recibo (receipt) or some kind of verification that it’s been cancelado (canceled). Tourists have been fined hundreds of dollars for inadvertently carrying uncanceled car-entry stickers on their windshields.

At the same time, return all other Mexican permits, such as tourist cards and hunting and fishing licenses. Also, be prepared for Mexico exit inspection, especially for cultural artifacts and works of art, which may require exit permits. Certain religious and pre-Columbian artifacts, legally the property of the Mexican government, cannot be taken from the country.

If you entered Mexico with your car, you cannot legally leave without it except by permission from local customs authorities, usually the Aduana (Customs House) or the Oficina Federal de Hacienda (Federal Treasury Office). (For local details, see Information and Services sections of the destination chapters.)

All returnees are subject to U.S. immigration and customs inspection. These inspections have become much more time-consuming since September 11, 2001. The biggest change is that all U.S. citizens must present a valid U.S. passport in order to re-enter the United States. On a good day, the wait amounts to about an hour. The worst bottlenecks are at the big border crossings, especially Tijuana and, to a lesser extent, Mexicali, Nogales, Ciudad Juárez, Laredo, and Brownsville.

U.S. law allows a fixed value (at present $400) of duty-free goods per returnee. This may include no more than one liter of alcoholic spirits, 200 cigarettes, and 100 cigars. A flat 10 percent duty will be applied to the first $1,000 (fair retail value, save your receipts) in excess of your $400 exemption. You may, however, mail packages (up to $50 value each) of gifts duty-free to friends and relatives in the United States. Make sure to clearly write “unsolicited gift” and a list of the value and contents on the outside of the package. Perfumes (over $5), alcoholic beverages, and tobacco may not be included in such packages.

Improve the security of such mailed packages by sending them by Mexpost class, similar to U.S. Express Mail service. Even better (but much more expensive), send them by Federal Express or DHL international couriers, which maintain offices in Puerto Vallarta, Tepic, and Manzanillo.

For more information on U.S. customs regulations important to travelers abroad, write for a copy of the useful pamphlet Know Before You Go, from the U.S. Customs Service (1300 Pennsylvania Ave., Washington, DC 20229, tel. 202/354-1000, www.cbp.gov). You can also order the pamphlet by phone or download it from their website (click on Travel at the bottom of the home page, then click on Know Before You Go.

Additional U.S. rules prohibit importation of certain fruits, vegetables, and domestic animal and endangered wildlife products. Certain live animal species, such as parrots, may be brought into the United States, subject to 30-day agricultural quarantine upon arrival, at the owner’s expense. The U.S. Customs Service’s Know Before You Go pamphlet provides more details on agricultural product and live animal importation.

For more information on the importation of endangered wildlife products, contact the Fish and Wildlife Service (1849 C Street NW, Washington, DC 20240, tel. 202/208-4717, www.fws.gov/).