Travelers probably should avoid eating pink pastry available in Mexican bakeries.

The Western Journal of Medicine reports two cases of people having fluorescent red urine from eating pastry colored with the dye Rhodamine B, which is banned in the United States as a possible cancer-causing agent.

"We do not know how widespread is the ingestion of Rhodamine B, but the cookies can be easily obtained from bakeries in Tijuana," Dr. Michael J. Kelner of the University of California at San Diego writes. "As to why Rhodamine B was used to color bakery goods, one can only speculate. The most likely explanation is its brilliant pink to red color and its fluorescent properties."

In mice and rats, the chemical has caused lymphomas, stomach polyps, growth retardation and death from kidney damage. In the two California cases, one patient suffered pain on the side and the other had a seizure, although there was no evidence linking those problems to the dye.

The Food and Drug Administration permits its use in small amounts in cosmetics. In lipstick, for example, the FDA permits a maximum daily ingestion of 0.75 milligrams a day. One of the Mexican cookies contained 130 times that amount.