To assess the characteristics of connective tissue metabolism in chronic renal failure (CRF), urinary excretion of glycosaminoglycan (GAG) fractions and hydroxyproline (HYP) was determined in ten patients with CRF and in ten age-matched healthy children. CRF was found to be associated with elevated free HYP (19.9 +/- 6.1 vs 9.8 +/- 3.6 mumol/day, P less than 0.05) and depressed peptide HYP excretion (33.1 +/- 13.5 vs 225.2 +/- 17.7 mumol/day, P less than 0.01), a low rate of total GAG excretion (7.0 +/- 2.4 vs 16.1 +/- 1.9 mumol uronic acid/day, P less than 0.05) with low chondroitin 4 -sulphate + chondroitin 6 -sulphate (Ch-Ss) (14.0 +/- 9.9 vs 65.0 +/- 22.1%) and a high proportion of non-sulphated or under-sulphated fractions, i.e. hyaluronic acid + chondroitin + heparan sulphate (HA + Ch + HS) (75.3 +/- 11.4 vs 31.5 +/- 5.7%). Urinary 3-methyl-histidine (3-met-HIS) excretion and plasma essential free amino acids did not differ in the two groups. In response to haemodialysis no consistent change occurred in urinary excretion of 3-met-HIS, peptide-bound HYP, total GAG or percentage distribution of individual GAG fractions. After haemodialysis all plasma amino acids decreased significantly, and there was a significant increase in urinary excretion of free HYP (P less than 0.05). We conclude that the alterations in urinary excretion of total and individual GAGs observed in CRF may reflect disturbed connective tissue metabolism which does not appear to be accounted for by protein malnutrition or enhanced protein breakdown and remains uninfluenced by haemodialysis therapy.