The capacity of Acanthocheilonema viteae to metabolize fructose was investigated in vitro. In common with other filarial species A. viteae oxidized fructose to lactate but its rate of consumption was only 40% of the glucose-containing control value. Fructose was not incorporated into glycogen. Release of 14CO2 from [U-14C]fructose was not detected in the presence of glucose and was about 40% of the glucose-containing value under conditions where fructose was the sole hexose substrate. Fructose consumption and lactate excretion increased in proportion to the external concentration of fructose. However, worm viability was not maintained in fructose over a 120 h in vitro incubation. In the presence of fructose, protein synthesis (measured incorporation of [35S]methionine into acid-insoluble material) was reduced compared to the glucose-containing control group; but was significantly greater than the value obtained under glucose-free conditions.