We have developed a method which can measure the menstrual prostaglandin (PG) activity in a single tampon specimen by bioassays. This method makes it possible to monitor the menstrual PG activity continuously during menstruation. Using this technique, we determined the menstrual PG patterns of two normal non-dysmenorrheic subjects, one subject on oral contraceptives (OC) and one subject with moderate to severe dysmenorrhea. Two to four cycles were studied per subject. We observed three mentrual patterns among the four subjects studied. Compared to the two normal controls, the subject on OC had a significantly lower menstrual fluid total and menstrual PG activity. The mean values +/- S.E. per menstrual period were 33.4 g +/- 1.5 vs 21.5 g +/- 2.0 and 28.6 microgram (PGF2alpha equivalent) +/- 1.5 vs 11.3 microgram +/- 4.2 respectively (control vs OC). The dysmenorrheic subject had a menstrual fluid total of 37.0 g +/- 1.9 similar to the two normal controls. Her menstrual PG activity (49.8 microgram +/- 7.7), however, was nearly two times higher than the normal controls. In one cycle studied, the dysmenorrheic subject was treated with a PG synthetase inhibitor, ibuprofen (Motrin). Remarkable relief was achieved. The alleviation of symptoms was accompanied by a concomitant marked reduction in the menstrual PG activity.