The ACL TOP is a fully automated random access analyser for coagulometric, chromogenic ou immunologic measurements. The aim of the present study was to evaluate its performances. The tests performed were: prothrombin time (PT), activated partial thromboplastin time (aPTT), prothrombin time derived fibrinogen (FibD), factor VIII (FVIII), antithrombin (AT) and free protein S antigen (PS). The comparison study was performed by analyzing patients samples in duplicate with ACL TOP and the analyser MDA II (BioMérieux) or CA 6000 (Dade-Behring). Imprecision (CV%) was < 4% for routine tests and < 5% for FVIII, AT and PS, except a between-run imprecision < 7,5% for low AT levels. The measured lower limits of linearity for FVIIII, AT and PS were satisfactory. The correlation observed between the ACL TOP and the other analysers was strict for PT and AT and good for TCA and FibD. Triglyceride levels > or = 6 mmol/L interfered with PT and FibD measurements. No sample or reagent carryover was observed in the conditions of the study. Overall, the ACL TO is an analyser with very satisfactory analytical and technical performances and is well suited for routine and specialized coagulation laboratories.