Sleep-disordered breathing is associated with chronic intermittent asphyxia and with a variety of cardiovascular abnormalities. Cardiovascular morbidity and mortality are linked to altered platelet function, and platelet function is affected in sleep-disordered breathing. As there is evidence that chronic continuous hypoxia may alter platelet number and function, the aim of the present study was to test the hypothesis that chronic intermittent asphyxia affects platelet count, activation and aggregation. Rats were treated with a hypercapnic hypoxic gas mixture (minimum of 6-8% O2, maximum of 10-14% CO2) for 15 s, twice per minute for 8 h per day for 3 weeks. Blood was analysed for platelet count, platelet activation (CD62p expression using flow cytometry), response to low dose ADP, haematocrit, red cell count and haemoglobin concentration. A platelet function analyser measured the closure time of an aperture, dependent on platelet aggregation. Compared to controls (n = 16), chronic intermittent asphyxia (n = 13) reduced body weight and increased right ventricular weight but had no significant effect on platelet count (control, 880.4 +/- 20.1; treated: 914.1 +/- 35.2 x 10(3) microl(-1); mean +/- S.E.M.), on the reduction in platelet count in response to ADP (control, reduced to 206.7 +/- 49.0; treated, reduced to 193.8 +/- 35.9 x 10(3) microl(-1)), or on the percentage of platelets positive for CD62p (control, 5.2 +/- 0.7; treated, 6.0 +/- 0.8%). Chronic intermittent asphyxia significantly (P = 0.037) reduced the closure time (control, 90.9 +/- 7.7; treated, 77.7 +/- 3.8 s), indicating greater adhesion and aggregation. There was no significant difference in haematocrit, red cell count and haemoglobin concentration. In conclusion, chronic intermittent asphyxia has no effect on platelet count but does increase platelet aggegation in rats. These data support the idea that chronic intermittent asphyxia alters platelet function in sleep-disordered breathing.