A study of the effect of (±)-4-diethylamino-1, 1-dimethylbut-2-yn-1-yl 2-cyclohexyl-2-hydroxy-2-phenylacetate monohydrochloride monohydrate (NS-21), a new drug for the treatment of urinary frequency and incontinence, was conducted in Crl:CD rats during the perinatal and lactational periods. Female rats(thirty-three per dose level) were given NS-21 orally at dose levels of 0 (control), 2, 25 and 300 mg/kg from day 17 of pregnancy to day 21 after delivery. All pregnant rats were allowed to deliver naturally for postnatal examination of their offspring. At the 300 mg/kg dosage level, reduced activity, salivation and rales were observed in dams, and five dams died. Decreases in body weight gain, food consumption and water consumption were also observed in the dams at the 300 mg/kg. The number of remaining implantation sites was increased at 300 mg/kg, indicating fetal morality. The number of live newborns, birth index and survival index at the birth were decreased at the 300 mg/kg dosage level. Reduced activity, paleness in color and/or discoloration were observed for many pups at the 300 mg/kg on lactation day 0. Body weights of male and female offspring at the birth were also decreased at the 300 mg/kg dosage group. Survival index at the 4 days was decreased at the 300 mg/kg dosage level. Body weight gains of male and female offspring were decreased at the 300 mg/kg during the lactational period and after weaning. NS-21 did not affect the postnatal development of the offspring, including physical and functional development, motor activity, emotionality, learning ability and reproductive performance. These results demonstrate that the NOAEL (no observed adverse effect level) of NS-21 is 25 mg/kg for general toxicity and reproductive function in mother rats and 25 mg/kg for developmental toxicity of their offspring.