PIP: Clinical research was carried out to determine the effect of PGs (prostaglandins), administered by different methods, on the midpregnant human uterus. The experiments were conducted on midpregnant women admitted to a Swedish hospital during the 14th-22nd week of pregnancy for therapeutic abortion. The laboratory procedures are explained and the results are graphed. A single intravenous injection of PGE1 or PGE2 caused an increment in uterine tone. The threshold dose for both these drugs was found to be approximately 20 mug. Intramuscularly administered PGE1 caused an elevation of uterine tone as well. 100 mug caused a long-lasting sustained contraction. Continuous intravenous infusion required 2 mug per minute. Intraamniotic and vaginal administration of PGE1 in high doses had no effect at all on the pregnant uterus.