The effects of warm bathing on short-term and circadian rhythms for blood pressure (BP), pulse rate (PR), and endocrine function were studied in 10 bed-ridden patients (5 men and 5 women; age 78.9 +/- 10.5 years old) hospitalized in Nomura Municipal Hospital. The results indicated a transient elevation of BP with bathing and its rapid fall after bathing. Compared with the days when patients did not take bath, systolic BP was significantly lower for 12 to 16 hours (p < 0.005) after bathing and diastolic BP was also significantly lower during 8 to 12 hours (p < 0.01), 12 to 16 hours (p < 0.001) and 20 to 24 hours (p < 0.001). The PR was significantly higher from 0 to 4 hours after bathing (p < 0.01), but became significantly lower during 8 to 12 hours (p < 0.001) and 12 to 16 hours (p < 0.001). Plasma renin activity increased significantly after bathing (p < 0.05). Thus, the effects of bathing in lowering BP of bedridden patients in stable condition may continue for several hours after bathing.