Objective: Assessment on platelet responsiveness to aspirin may be required in selected clinical conditions. So far, no standardization in laboratory practices for aspirin assessment using whole blood (WB) platelet aggregation based test. A study for method validation was performed to investigate the aspirin effects on platelets by comparing with a reference method.Methods: Forty patients taking aspirin were analyzed using WB by conventional platelet aggregometer (Chrono-Log Model 500CA/560CA). Among these patients, nine of them had their platelet rich plasma (PRP) tested by the same analyzer (reference method). Another WB specimens from 25 patients were tested on both ChronoLog and Multiplate® (Dynabyte GmbH), which is a newer generation platelet function analyzer.Results: There were good and moderate agreements between WB on the Chronolog analyzer vs the reference method and WB on Chronolog vs WB on Multiplate® analyzers respectively.Conclusions: There are agreements between PRP and WB aggregation (WBA) methods in detecting aspirin effects on platelets. It is recommended that the test validation for the assessment of platelet responsiveness to aspirin is interpreted and correlated with the reference method preferably PRP.