Sex steroid hormones secreted by the gonads play a central role in the reproduction of all vertebrates. In addition to direct effects on gametogenesis, sex steroid hormones are important in sexual development, brain organization, and sexual behavior. The actions of sex steroid hormones are mediated primarily by ligand-dependent transcription factors, or receptors which bind to specific sequences of the DNA and alter the transcription rates of nearby genes. We have used the polymerase chain reaction to amplify cDNA fragments of the estrogen receptor, progesterone receptor and androgen receptor from the unisexual whiptail lizard, Cnemidophorus uniparens. The lizard steroid hormone receptors share a high degree of sequence homology to the steroid hormone receptors of other vertebrates. Ribonuclease protection assays demonstrate that both estrogen receptor mRNA and progesterone receptor mRNA are increased in the oviduct during vitellogenesis and after estrogen treatment. This report demonstrates the utility of the polymerase chain reaction to generate species specific probes for comparative molecular studies and provides the first report of cDNA sequences for reptilian steroid hormone receptors.