Substrate candidates for calcineurin, a serine/threonine phosphatase, have been screened by yeast two-hybrid assays. We found that a 85 kDa basic protein interacted with the catalytic domain of TAX-6. The calcineurin interacting protein, cnp-2, is expressed in head neurons, posterior intestine, spermatheca-uterus valve in hermaphrodites, and in spicule retractor neurons, rays and at the end of fan, which are mating behavior-mediated organs, in males. cnp-2 is required in the ovulation, arrangement of eggs, ray structure and mating behaviors, and is critical in the mating efficiency and sperm activation. Expression of IP3 signaling molecules was significantly decreased in hermaphrodite reproductory organs of cnp-2 mutants, which suggest that IP3 signaling is suppressed when cnp-2 was absent. We are currently further investigating functions of cnp-2 on reproductive process.