Differences in gene expression between benign and malignant human prostate specimens were investigated using the differential display technique. RNA samples from paired benign and malignant areas microdissected from opposite sides of the same prostate gland were used for reverse transcription PCR. A 477-bp band was identified that was consistently present in benign prostate but absent or diminished in intensity in malignant tissue. This band was cloned, and the sequence demonstrated 99% identity with a region in the fourth exon of the human neurofilament heavy chain gene (NF-H). Northern blotting with a cDNA probe derived from this band confirmed the presence of a similarly sized message of approximately 3.9 kb in both prostate and brain, and reverse transcription PCR using primers specific to an upstream region of exon 4 confirmed NF-H-like mRNA expression in benign prostatic tissue. Immunostaining with a monoclonal antibody to NF-H showed a positive reaction in benign prostatic epithelial cells but complete absence of staining in prostatic cancer cells. These data demonstrate the presence of a NF-H-like gene product in normal prostatic epithelial cells that is down-regulated or absent in prostatic carcinomas.