The influence of various pathological conditions on fructosamine levels in normoglycaemic dogs and cats was investigated. The most frequent and most pronounced deviations were found in animals with hypoproteinaemia, in which fructosamine was significantly lower than in the controls. In 66 per cent of the dogs and 67 per cent of the cats with hypoproteinaemia the levels were below the reference range. In the dogs the concentration of fructosamine was correlated with the level of albumin, but in the cats it was correlated with the level of total protein. Dogs with hyperlipidaemia and azotaemia also had significantly lower levels of fructosamine; 38 per cent of those with hyperlipidaemia and 47 per cent of those with azotaemia had fructosamine levels outside the reference range. No significant changes in fructosamine were detected in dogs or cats with hyperproteinaemia or hyperbilirubinaemia, or in cats with hyperlipidaemia or azotaemia.