Vibrio vulnificus cytolysin caused platelet cytolysis and increased intracellular calcium concentration ([Ca2⁢]]i) of rat platelets in a concentration-dependent manner. In the presence of V. vulnificus cytolysin (3 HU/ml), lactate dehydrogenase (LDH) activity was increased from 1.3⁑0.4% of control to 64.3⁑3.4% in platelet suspension buffer. In Ca2⁢-free platelet suspension buffer, however, V. vulnificus cytolysin did not induce [Ca2⁢]i increase and LDH release. Addition of EGTA (2 mM) to suspension buffer after the initial Ca2⁢ influx reversed [Ca2⁢]i to the control level. However, a Ca2⁢ channel blocker verapamil (20 μM) or mefenamic acid (20 μM) did not inhibit V. vulnificus cytolysin-induced [Ca2⁢]i increase and LDH release. Divalent cations such as Co2⁢, Cd2⁢ or Mn2⁢ (2 mM each) also did not alter V. vulnificus cytolysin-induced [Ca2⁢]i increase and LDH release. V. vulnificus cytolysin (3 HU/ml)-induced calcium influx was completely blocked by lanthanum (2 mM). Lanthanum (2 mM) also completely blocked V. vulnificus cytolysin (3 HU/ml)-induced LDH release. Osmotic protectants such as, raffinose, sucrose or PEG600 (50 mM each) did not inhibit the lytic activity of V. vulnificus cytolysin. In conclusion, lanthanum sensitive Ca2⁢ influx plays a significant role in Vibrio vulnificus cytolysin-induced platelet cytolysis and thrombocytopenia in V. vulnificus infection.