Pontier J-M, Blatteau J-E, Vallée N. Blood platelet count and severity of decompression sickness in rats after a provocative dive. Aviat Space Environ Med 2008; 79:761–4. Introduction: Previous animal studies reported that platelet count (PC) is decreased following decompression. Adherence and aggregation of platelets to the bubble surface has been demonstrated in severe decompression sickness (DCS). The present study was designed to clarify the relationship between post-dive platelet levels and the severity of DCS in a rat model. Methods: A total of 57 male Sprague-Dawley rats were assigned to either one experimental group with a hyperbaric exposure (N = 22) or one control group (N = 27). Rats were compressed to 1000 kPa (90 msw) for 45 min while breathing air and decompressed to surface in 38 min with stops at 200, 160, and 130 kPa. Onset of neurological DCS and death time were recorded during a 120-min observation period after surfacing. In the control group, rats were maintained at atmospheric pressure in the same chamber for an equivalent period of time. Blood samples for PC were taken 30 min before and immediately after exposure in two groups. Results: Blood PC after hyperbaric exposure had significantly decreased, whereas PC had increased in the control group. We found a correlation between % fall in PC and latency to death time. The platelet loss tended to decrease when fatal DCS was delayed. Rats suffering from severe DCS with a short latency to death presented a pronounced decline in platelets. Discussion: The present study highlighted a relationship between the post-dive decrease in PC and DCS severity in rats. Platelet consumption could offer a new index for evaluating decompression stress.