Dysmenorrhoea is a recurrent painful disease which causes physical and psychological stress. The purpose of the present study was to investigate whether there was a measurable derangement of immune cells and immune responses in women with severe primary dysmenorrhoea. On day 26 of one cycle and on days 1 and 3 of the following cycle we measured polyclonal, mitogen-induced lymphocyte proliferation and beta-endorphin concentration in peripheral blood mononuclear cells obtained from 16 infertile women with normal pelvis, of whom eight had and eight did not have the disorder. In women with dysmenorrhoea, polyclonal mitogen-induced lymphocyte proliferation was lower than in controls on all 3 days considered, but the difference was statistically significant only on day 26 (43,605 +/- 9876 micrograms/ml versus 67,305 +/- 15,249 micrograms/ml; P < 0.01). Monocyte beta-endorphin concentrations in the patients with dysmenorrhoea were significantly elevated on day 3 compared to controls (67.8 +/- 24.3 pg/10(6) cells versus 29.7 +/- 6.9 pg/10(6) cells; P < 0.05). Our results demonstrate that immune responses are modified in patients with primary dysmenorrhoea. These effects are independent of circulating hormone concentrations and are consistent with the role of dysmenorrhoea as a stressful event.