Northern analysis shows that Go alpha mRNA is highly expressed in immature germ cells from rat. Whereas alpha o2 mRNA is the major form in pachytene spermatocytes, a message of shorter chain length is present in large amount in haploid germ cells. This mRNA was detected with an oligonucleotide specific for the 3'-coding region of alpha o2, but did not hybridize to oligonucleotides specific for the 5'-untranslated and 5'-coding regions. The results indicate the presence of a novel splice variant of alpha o mRNA, which may code for a Go alpha protein important for germ cell development.