Primary dysmenorrhea is a common gynaecological symptom complex characterized by a painful syndrome occurring predominantly on the first and the second day of the cycle and associated with concomitant autonomic phenomena. In a randomized double-blind study, the therapeutic effect of magnesium has been investigated in 32 women (16 to 42 years old) who have been treated in the gynaecological outpatient-department at our clinic because of primary dysmenorrhea. The dosage of Magnesiocard comprised 3 X 5 mmol granulate orally on the day preceding menstruation and on the first and the second day of the cycle. At the end of the study, which covered six cycles, we were able to analyze the results in 21 patients, 11 having been treated with magnesium and 10 with placebo. While in the magnesium group only a slight effect was noted on the first day of the cycle under therapy when compared to both the placebo group and the dysmenorrhea disturbances persisting before therapy was started, magnesium had a therapeutic effect on both back pain and lower abdominal pain on the second and the third day of the cycle. Parallel to this therapeutic influence on the symptomatology of dysmenorrhea, a marked reduction in absences from work due to the dysmenorrhea was also noted. The possibilities of magnesium therapy in dysmenorrhea should be investigated further in multicentre studies.