We have established a new chemiluminescent enzyme immunoassay for Carcinoembryonic antigen (CEA), designated ACCESS CEA, which is adapted to the fully automated ACCESS® immunoassay analyzer. The assay is based on a one step sandwich-type method using two monoclonal antibodies, one of which is immobilized on micrometer-size paramagnetic particles and the other is conjugated to alkaline phosphatase. Ten microliters of calibrators or sera are incubated for 5 minutes at 37 °C with the particles and with the alkaline phosphatase conjugate. The particles are then magnetically separated and washed to remove unbound components. Time needed to obtain the first result is less than 15 minutes.The assay range was 0.04-1000 μg/l of CEA, and the possible high-dose hook effect was prevented at CEA concentrations up to 100000 μg/l in this working range. The coefficient of variation (CV) for intra-assay precision was 3.0 to 4.7%, and inter-assay CV was 3.4 to 5.6%. The sample carryover was less than 0.001%. The analytical recovery ranged from 98 to 104% and a dilution linearity was demonstrated. No interference was detected in any sample with levels up to 300 mg/1 for bilirubin, 12000 mg/1 for haemoglobin, 50000 mg/1 for human serum albumin, 8 500 mg/1 for triacylglycerol, and 500 000 IU/1 for rheumatoid factor. The ACCESS CEA assay also showed very homogeneous reactivity with purified CEA preparations from different tumours and could discriminate CEA from four CEA-related normal antigens tested.Serum samples (n = 362) from patients with malignant or non-malignant disease, as well as from healthy individ-