Fourteen normal women (self-selected from 180 women enrolled) in a marathon training clinic kept basal body temperature (BBT), mileage, and weight records for 48 cycles before the marathon. Entry criteria were: Age 20-45, gynecologic age greater than 5 years, no hormone use, or weight change in 3 months. The women were 35.2 +/- 5.6 years in age, 22.6 +/- 5.1 years gynecologic age, runners of 4.1 +/- 2.5 years with premenstrual symptoms, previous pregnancy 4/14, no infertility and 2/14 remote amenorrhea. BBT records were obtained and analyzed by Vollman's criteria (1977). There was no weight loss. 32/48 cycles were biphasic but only 16 were normal in the length of the premenstrual phase (PreM = luteal, nl 10 - 16 d) with a mean of 11.1 +/- 1.2 days. The other 16 biphasic cycles had short PreM phase of 6.4 +/- 1.8 days. Monophasic (M = anovulatory) cycles occurred in 16/48 records. Cycles which were abnormal (Short PreM and M) differed only in that usual run length was longer (9.6 - 9.9 miles) than in normal cycles (7.9 +/- 2.4 miles). Marathon training may be associated with normal length but M and short PreM type cycles.