The purpose of the study was to investigate the in vitro bactericidal function of blood polymorphonuclear leucocytes (PMN) in various phases of the menstrual cycle from otherwise healthy women with recurrent cutaneous abscesses related to the premenstrual phase of the menstrual cycle compared with the bactericidal activity of PMN from healthy women with no inconveniences related to the menstrual cycle. The bactericidal activity against Staphylococcus aureus 502A was investigated and when possible against the patients' own strain. No variation in bactericidal activity was observed during the different phases of the menstrual cycle. PMN from five women with recurrent abscesses related to the premenstrual phase tended to kill fewer S. aureus 502A than PMN from three women in the control group. The literature of immunological defence mechanisms and the occurrence of infections related to the menstrual cycle is reviewed.