Objective: To investigate pain perception and the potential analgesic effects of mindful states in experienced Zen meditators. Methods: Highly trained Zen meditators (n 13; 1000 hours of practice) and age/gender-matched control volunteers (n 13)received individually adjusted thermal stimuli to elicit moderate pain on the calf. Conditions included: a) baseline-1: no task; b) concentration: attend exclusively to the calf; c) mindfulness: attend to the calf and observe, moment to moment, in a nonjudgmental manner; and d) baseline-2: no task. Results: Meditators required significantly higher temperatures to elicit moderate pain (meditators: 49.9°C; controls: 48.2°C; p .01). While attending “mindfully,” meditators reported decreases in pain intensity whereas control subjects showed no change from baseline. The concentration condition resulted in increased pain intensity for controls but not for meditators. Changes in pain unpleasantness generally paralleled those found in pain intensity. In meditators, pain modulation correlated with slowing of the respiratory rate and with greater meditation experience. Covariance analyses indicated that mindfulness-related changes could be partially explained by changes in respiratory rates. Finally, the meditators reported higher tendencies to observe and be nonreactive of their own experience as measured on the Five Factor Mindfulness Questionnaire; these factors correlated with individual differences in respiration. Conclusions: These results indicated that Zen meditators have lower pain sensitivity and experience analgesic effects during mindful states. Results may reflect cognitive/selfregulatory skills related to the concept of mindfulness and/or altered respiratory patterns. Prospective studies investigating the effects of meditative training and respiration on pain regulation are warranted. Key words: pain, meditation, Zen, mindfulness, respiration, psychophysics.