Functional evidence indicates that voltage-dependent Ca 2+ (Ca v) channels participate in sea urchin sperm motility and the acrosome reaction (AR), however, their molecular identity remains unknown. We have identified transcripts for two Ca 2+ channel α1 subunits in sea urchin testis similar in sequence to Ca v1.2 and Ca v2.3. Antibodies against rat Ca v1.2 and Ca v2.3 channels differentially label proteins in the flagella and acrosome of mature sea urchin sperm. The Ca v channel antagonists nifedipine and nimodipine, which inhibit the AR, diminish the intracellular Ca 2+ elevation induced by a K +-induced depolarization in valinomycin-treated sperm. These findings reveal that Ca v1.2 and Ca v2.3 channels could participate in motility and/or the AR in sea urchin sperm.