As part of an evaluation of a Synchron CX5 analyser (Beckman Instruments Inc, Brea, USA) we examined a range of tests for interference from haemolysis, bilirubin and lipaemia. Tests investigated were urea, creatinine, urate, total protein, albumin, calcium, total bilirubin, alkaline phosphatase (ALP), aspartate transaminase (AST), gamma-glutamyl transferase (GGT) and inorganic phosphate. Two types of interferences were found. One type is found on other analysers and represents analytical difficulties with the measurement of that particular analyte. The other type of interference was a consequence of the bichromatic optical system used on the CX-5. This latter group includes haemoglobin interference in the measurement of total protein and inorganic phosphate, and bilirubin interference with the measurement of total protein, glucose and inorganic phosphate. Lipaemia interfered with total protein, total bilirubin, inorganic phosphate, urate and glucose. Alternative and modified methods are proposed to improve the measurement of total protein, glucose, total bilirubin and inorganic phosphate. The use of the modified methods for glucose, inorganic phosphate and total bilirubin are limited, at this time, by an error in the calculation algorithm used by the analyser for two step or triggered chemistries, and to a lesser extent, by a reduction in sample throughput.