Platelet aggregation in response to ADP, adrenaline, collagen, arachidonic acid and ristocetin was measured in a large population of healthy Saudi males (n = 393) and females (n = 221) whose age ranged from 11–60 years. The number of observations ranged from 130 for one of the doses of ristocetin (1.0 g/l) to 554 for one of the doses of ADP (2.0 mol/l). Females exhibited more enhanced aggregation responses than males. Blood groups, smoking and body weight had no significant effect on platelet aggregability. No significant variations were noted when morning versus afternoon measurement were compared. The results are discussed and compared to previous reports based on small population studies. The data obtained represent the normal pattern of platelet aggregation in healthy Saudis.