Polyamines in plasma, urine, and amniotic fluid during pregnancy in rats were measured using high performance liquid chromatography (HPLC). Putrescine and spermidine in the plasma, and putrescine and spermine in the urine were elevated during pregnancy. The sharp increase in putrescine in the late stage of pregnancy in body fluids was particularly characteristic. Slight increases in plasma and urinary spermine levels were observed in the early stage of pregnancy. It was found that the administration of the steroid hormones, progesterone, estradiol-17 beta, and estriol, to virgin rats did not influence the concentrations of urinary polyamines, and that urinary putrescine levels did not rise in experimental IUGR rats, but they rose in the urine of the sham operation group. These data suggest that changes in polyamines in plasma, urine, and amniotic fluid were possibly subject to fetal growth and/or functional differentiation more than hormonal regulation during rat pregnancy.