OBJECTIVE Effect of a single dose of cyclophosphamide on migration of the primordial germ cells (PGC), when they are about to reach gonadal ridge was investigated histochemically by staining for alkaline phosphatase. This may throw some light on the fate of gonadal ridge when exposed to the drug itself or its breakdown products such as acrolein, which is present as an environmental pollutant. METHODS Twelve pregnant Charles foster rats were divided in to control and treatment groups and kept in separate cages. In the experimental group, Cyclophosphamide 20 mg/kg/body weight was injected intraperitoneally on day 12 of gestation. Transverse sections of fetuses collected on day 16 of gestation were stained for alkaline phosphatase activity. Outcome of the study was analysed by scanning the photomicrographs and represented by photomicrographs. RESULTS An unique finding in experimental group in the gonadal ridge consisted of homogeneously distributed pale staining cells. The gonadal ridge-mesonephros junction showed a single big cluster of the PGC. Under higher magnification, the PGC could be identified by oval or circular shape with well-defined cell membranes and very distinct dark brown staining. There were no signs of degeneration or disintegration of these cells. CONCLUSIONS Cyclophosphamide exposure led to failure of PGC to spread inwards from the gonadal ridge-mesonephros junction giving rise to a situation so far not reported in literature. The presented phenomenon will result in improper development of the gonads leading to infertility in an affected individual in future generation (Fig. 4, Ref. 18).