In a study of the influence of nutritional state on halothane anaesthesia, results were obtained which showed how the blood/gas partition coeffecient for halothane varied with blood chemistry in 20 patients undergoing elective surgery. For each patient the partition coefficient λ was measured by equilibration at 37 °C of a blood sample with a 1% halothane in 5% carbon dioxide in air mixture, followed by chemical extraction and estimation of the halothane content by gas chromatography. The haematocrit and haemoglobin, serum albumin, total protein, triglyceride and cholesterol concentrations were measured by routine laboratory methods. Regressions were sought of λ on each of these, and on the globulin concentration and the ratios of albumin : globuin and albumin : total protein, deduced from these determinations. The only statistically significant regression (P = 0.0004) was that of λ on the serum triglyceride concentration (T) (mmol/litre): λ = 1.83+0.424T. The dependence of λ on haemoglobin concentration was not statistically significant, but the slope of the regression was consistent with those of previous investigators. The regressions of λ, corrected to the mean triglyceride concentration, on the ratios of albumin : globulin and albumin : total protein were not statistically significant but were not significantly different from an earlier reported result.