It has been reported that thalidomide, dissolved in a 1:3 mixture of Tween 20 and physiological saline and administered intraperitoneally to pregnant mice and rats induces a variety of malformations, including limb deformaties, characteristic of the primate syndrome. The studies reported herein attempted to confirm these findings without success although the rodent strains used were not the same. A low level of non-specific malformations was observed in the fetuses of both species at dose levels reported to cause a 47 percent and 92 percent rate of malformation in mice and rats respectively. One possible source of difference was Tween 20 which was toxic to the point of lethality in these studies at dose levels reported to be non-toxic in the earlier studies.