We retrieved a series of measurements made 35 years ago of the concentration of inorganic phosphate (P) in the serum from 56 cases of severe protein-energy malnutrition at the Tropical Metabolism Research Unit, Jamaica. There is no record of whether or not the cases were randomly selected. The samples were obtained within 4 days of admission and except in 3 cases there was no follow-up. The average age was 12 months. The children have been classified retrospectively from the notes as marasmus (11 cases), kwashiorkor (22 cases) and marasmic kwashiorkor (23 cases). In all 11 children died (fatality rate 20%), eight of them from the group with marasmic kwashiorkor. Weight-for-age, length-for-age and weight-for-length have been calculated as Z-scores. Nearly all serum phosphate concentrations were low (mean 1.41 mmol.l-1, SD 0.444, range 0.50-2.45) compared with the normal value at this age of about 2 mmol.l-1. The serum P was significantly less depressed in the marasmic children (P = 0.042), but there was no relation between serum P and any of the anthropometric measurements, nor with outcome (death or survival). There was, however, a significant relationship with the degree of oedema. Death was related to age--the children who died were younger (mean difference 3.8 months; P = 0.01; 95% confidence interval 0.23-6.43). It took about 3 weeks of feeding a milk-based diet for serum phosphate to reach normal levels. There have been few previous measurements of serum P in malnutrition.(ABSTRACT TRUNCATED AT 250 WORDS)