To disclose the relationship between tea consumption and lung cancer risk, we analyzed the data from a case-control study conducted in Okinawa, Japan from 1988 to 1991. The analysis, based on 333 cases and 666 age-, sex- and residence-matched controls, provided the following major findings. (a) The greater the intake of Okinawa tea (a partially fermented tea), the smaller the risk, particularly in women. For females, the odds ratios (and 95% confidence intervals) for those who consumed 1-4, 5-9, and 10 cups or more of Okinawan tea every day, relative to non-daily tea drinkers, were 0.77 (0.28-2.13), 0.77 (0.26-2.25) and 0.38 (0.12-1.18), respectively (trend: P = 0.032). The corresponding odds ratios for males were 0.85 (0.45-1.55), 0.85 (0.45-1.56) and 0.57 (0.31-1.06) (trend: P = 0.053). (b) The risk reduction by Okinawan tea consumption was detected mainly in squamous cell carcinoma. Daily tea consumption significantly decreased the risk of squamous cell carcinoma in males and females, the odds ratios being 0.50 (95% confidence interval 0.27-0.93) and 0.08 (0.01-0.68), respectively. These findings suggest a protective effect of tea consumption against lung cancer in humans.