A case-control study of bladder cancer involving interviews with 111 incident cases and 222 controls was carried out in Montevideo, Uruguay. The analysis was conducted separately for each sex. Point estimates of relative risk associated with smoking variables, ingestion of infusions of the herb Ilex paraguariensis (maté), and selected dietary items were obtained by stratified and logistic regression analysis. Among men, smokers of black tobacco showed a relative risk (RR) 2.7 higher than blond tobacco smokers and maté exposure showed a significant dose-response, after adjustment for age, residence, social class, hospital, type of tobacco, smoking intensity, smoking duration, and vegetable consumption, with a seven-fold increase in risk for heavy consumers. Joint exposure to type of tobacco and maté consumption showed a multiplicative effect. Women showed a similar increase in risk with maté consumption. The results suggest that the high mortality rates of bladder cancer observed in Uruguay could be explained by the combined effect of black tobacco smoking and maté ingestion.