The selective and destructive action of a single subcutaneous injection of cadmium chloride on the testes of various laboratory animals was first described by Pařízek in 1956 (see Pařízek, 1957). These observations have been confirmed and extended in a number of laboratories (Cameron & Foster, 1963; Chiquoine, 1964; Gunn, Gould & Anderson, 1961, 1963; Kar & Das, 1960; Mason, Brown, Young & Nesbit, 1964; Meek, 1959; Pařízek, 1957). On the other hand, no effect of such an injection on the female reproductive system was noted (Gunn et al., 1961; Pařízek, 1960). Recently Pařízek (1964) has reported that a single subcutaneous injection of 0·04 mm CdCl2/kg body weight given to pregnant rats on the 17th to 21st day of pregnancy resulted in destruction of the foetal portion of the placenta and death of the embryos. The study reported here documents the sensitivity of the pregnant albino mouse to