Cholesterol values measured with the Reflotron(R) dry chemistry (Boehringer Mannheim, Mannheim, Germany) and enzymatic (CHOD-PAP) routine method in 4150 venous blood samples from 580 infants aged 7 months, 1778. children aged 13 months to 19 years, and 1792 adults aged 18-63 years showed good correlation between the two assay systems (r > 0.92). However, the mean cholesterol concentrations were 4.5%, 3.7% and 2.3% lower in infants, children and adults, respectively, if measured with the Reflotron analyser as compared with values obtained with the CHOD-PAP method. These differences in the values were greater when cholesterol values were low (significance for the slope of regression line, p < 0.001). Values were below the detection limit of the Reflotron assay (2.59mmol l-1) in 104 (4.4%) and 4 (0.2%) of all paediatric and adult samples, respectively. When measured with the CHOD-PAP method, 75 (72%) and 3 (75%) of these same samples showed values which exceeded the 2.59mmol l-1 detection limit. We conclude that Reflotron dry chemistry analyser is precise in fast measurement of serum cholesterol both in all paediatric subjects and adults. A particular problem in paediatric age groups is that about 4% of children have values below the detection limit of the Reflotron analyser.