Acute toxicity studies of propiverine hydrochloride (P-4) were carried out in mice, rats and dogs of both sexes. 1. The LD₅₀ values of P-4 were as follows : Mice ; 410(male) and 323(female) mg/kg in oral route, 223(male) and 283(female) mg/kg in subcutaneous route and 36(male and female) mg/kg in intravenous route, Rats ; 1000(male) and 1092(female) mg/kg in oral route, 1632(male) and 1411(female) mg/kg in subcutaneous route, and 22(male) and 25(female) mg/kg in intravenous route. On the LD₅₀ values, no sexual difference was apparent but the species difference between mice and rats observed to be present in oral and subcutaneous routes. The approximate lethal doses of P-4 in dogs were 987-1137 mg/kg for male and 865-894 mg/kg for female in oral route, and the values were almost same as those in rats of oral route. 2. Major toxic signs such as clonic convulsion, bradypnoea, dyspnoea, decreased spontaneous activity and hematuria were observed in mice and rats. Furthermore mydriasis in rats, and transitory salivation and/or vocalization in mice and rats were observed. In some rats, sedation, salivation, soil at hypogastrium, rale and emaciation were detected from the next day of oral administration. In dogs, toxic signs such as vomiting, tremor, tonic and/or clonic convulsion, mydriasis and gasping were observed. 3. Pathological changes observed in dead animals were congestion of lungs, liver and kidneys in all routes, congestion and hemorrhage in digestive tracts in oral route, inflammatory changes at the injection site in subcutaneous route. In addition, retention of hematuria in urinary bladder in rats of oral and subcutaneous routes, the hemorrhagic changes of heart, atonia of urinary bladder and retention of urine in dogs were observed. 4. The main cause of death seemed to be respiratory disturbance in all species and the weakness in a few rats of oral route.