To evaluate its clinical value, the half-life of caffeine (1,3,7-trimethylxanthine) in saliva (SCT) after 3 mg/kg-1 oral caffeine was measured in 53 children with chronic liver disease (mean age, 4.41 years) and 48 control children (mean age, 6.26 years) in five samples over 24 h and compared with parameters of liver function and outcome. Sensitivity was 60.3% and specificity 97% of SCT for diagnosis of chronic liver disease. The correlation of SCT with serum albumin (ALB) was -0.52 (p < 0.001), total bilirubin (SBR) was 0.585 (p < 0.001), prolonged prothrombin time (PT) was 0.387 (p = 0.004), and aspartate aminotransferase (AST) was 0.538 (p = 0.001). The correlation of SCT with a clinical score of liver dysfunction calculated from the presence of features of hepatic decompensation was 0.627 (p < 0.001) and with Malatack's paediatric prognostic score was 0.505 (p < 0.001). Serial SCT and liver function tests were performed on 53 patients on 127 occasions during a mean follow-up of 361 days (range, 4-709). Of this group, 18 were listed for liver transplantation. Predictive values of outcome by analysis of variance expressed as ratio of mean squares were SBR, 34.1 (p < 0.001); log10 SCT, 20.6 (p < 0.001); ALB, 5.2 (p < 0.05); PT, 1.2 (NS). SCT correlated with clinical and biochemical parameters of severity of liver disease, but SBR was a better predictor of listing for liver transplantation in this group of paediatric patients.