Luteinizing hormone/chorionic gonadotropin (LH/CG) receptor complementary DNA (cDNA) isoforms were amplified using pseudopregnant rat ovarian total RNA as a template and the primers reaching over the coding regions at both ends in a reverse transcriptase-polymerase chain reaction (RT-PCR). Agarose gel electrophoresis of the PCR products revealed three bands corresponding to about 2.1, 2.0 and 1.8 kilobases (kb). Subcloning of pooled PCR products into EcoRI site of pUCBM20 resulted in 167 clones, from which five different restriction patterns were obtained by digestion with EcoRI and HaeIII. One clone of each was further characterized. It could be predicted from the nucleotide sequences that the clone rLHR2100 encoded a full-length receptor (a 674 amino acid mature protein), the clone rLHR2075 lacked part of exon IX (nucleotides 693-717) and encoded a truncated 225 amino acid mature protein, the clone rLHR1950 lacked exons III and IV (nucleotides 246-395) and encoded a nearly full-length protein (a 624 amino acid mature protein), and the clones rLHR1834 and rLHR1759 lacked the same part of exon XI (nucleotides 960-1225), with exon V (nucleotides 396-470) also absent in the latter, the deletion in exon XI leading both these clones to premature termination. The clone rLHR1834 encoded a 316 amino acid mature protein and rLHR1759 a 291 amino acid mature protein, respectively. The sequence data suggest that all of these isoforms contain the putative signal sequence and are derived from a single copy gene via alternative splicing. These results point further to the fact that the expression of the 90 kDa LH/CG receptor is regulated via an extensive alternative splicing of the receptor gene primary transcript.