In a previous report we presented a modification of the original Differential Display PCR technique using a single oligo (dT) primer for the reverse transcription reaction (instead of the various oligo (dT)NM primers that subdivide the pool of mRNAs) and a combination of 25-mer or 26-mer arbitrary primers together with 30-mer anchored primers for the PCR reaction. The PCR products were, then, efficiently separated in a nondenatuting polyacrylamide gel and the bands were visualized after staining with silver nitrate. In this report we extended our studies and we used fish gonads from various fish as the model to trace the differential expression of mRNAs, which were isolated by various methods. Since xenoestrogens are toxic to the gonads of many fish, we tried to set up the conditions in order to further characterize genes that are markers of exposure to xenoestrogens