Aims: The lipid composition of platelets and the function of these cells in patients with uremia were studied. Methods: Fourteen patients and 14 normal volunteers were studied. Platelet lipids including phospholipids and cholesterol, as well as the platelet aggregation response to agonists, were studied. Results: The amount of platelet phospholipids was decreased in patients compared to controls (338.0 ± 79 vs. 511.6 ± 125 nmol/10<sup>9</sup> cells; p < 0.001), while the percentage of the five main specimens of these compounds was normal. The content of platelet cholesterol in patients (97.8 ± 17.0 µg/10<sup>9</sup> cells) was similar to that in controls (91.7 ± 26.0 µg/10<sup>9</sup> cells). Consequently, the cholesterol:phospholipid ratio in uremic platelets was increased (0.75 ± 0.1 vs. 0.46 ± 0.1; p < 0.01). Although this feature is associated with hyperreactive platelets, the aggregation tests were defective for adenosin diphosphate (p < 0.01), arachidonic acid (p < 0.01), epinephrine (p < 0.01) and collagen (p < 0.001). This behavior is probably due to the multifactorial platelet defect described in uremia.