We have used PCR to isolate and characterise Leydig insulin-like peptide (Ley I-L) mRNA from sheep ovary. The deduced amino acid sequence of sheep Ley I-L has good homology with the pig and human peptides, having 93% and 77% amino acid identity, respectively. Northern blot analysis revealed abundant expression in both ovary and testis. An examination of ovarian RNA from non-pregnant and pregnant sheep showed that pregnancy did not significantly increase Ley I-L mRNA levels. However mRNA levels did alter depending on whether ovaries contained a corpus luteum. Also ovaries were examined by hybridisation histochemistry to locate the site of expression. Abundant Ley I-L mRNA levels were found in the theca interna cells of the ovary.