A cDNA encoding for an antigen, designated as NZ-3, was cloned and sequenced from human testis. The 1481-bp NZ-3 cDNA yielded an open reading frame (ORF) of 231 amino acids (aa) with the first ATG, Met start codon at nucleotide (nt) 104 and the stop codon TGA at nt 797. Extensive computer search indicated it to be a novel cDNA/protein. The ORF of NZ-3 cDNA was subcloned into pGEX-1 lambdaT vector and expressed in glutathione S-transferase gene fusion system. The expressed recombinant protein had a molecular size of similar to 25 kDa, and the rabbit antibodies (Ab) against the recombinant antigen recognized a specific protein band of 63 +/- 3 kDa in the human testis extract. The NZ-3 antigen was located on the acrosomal and tail regions of human sperm cell and the NZ-3 Ab significantly (P < 0.001) inhibited human sperm capacitation and/or acrosome reaction. The novel recombinant NZ-3 antigen may find applications in immunocontraception and in specific diagnosis of human infertility.