Using a synthetic oligonucleotide primer complementary to human prostate-specific antigen mRNA, we found that an additional sequence possibly similar to human glandular kallikrein-1 could be read by a primer-extension sequencing technique. We were able to confirm the identity of that additional sequence with another oligonucleotide primer complementary to a specific region of the human glandular kallikrein-1 mRNA sequence. Northern blot analysis with 2 oligonucleotide probes respectively specific for prostate-specific antigen and human glandular kallikrein-1 mRNAs showed that the length of both mRNAs was similar at 1.5 kb. The level of human glandular kallikrein-1 mRNA relative to that of prostate-specific antigen could be estimated as approx. 10-20%. This study constitutes the first evidence that the human glandular kallikrein-1 gene is expressed at a high level in a human tissue.