The administration of L-carnitine to patients undergoing hemodialysis increases hematocrit and improves the response to recombinant human erythropoietin (rhEPO). This suggests a contribution by carnitine to erythrocyte membrane function or erythropoiesis. We investigated the effect of L-carnitine and palmitoyl- L-carnitine on erythropoiesis by assessing erythroid colony formation in in vitro fetal mouse liver cell cultures. L-Carnitine or palmitoyl- L-carnitine was added with rhEPO to fetal mouse liver cell cultures. Doses of L-carnitine of up to 200 µmol/l to the culture had no effect on colony formation. In contrast, the addition of above 12.5 µmol/l palmitoyl- L-carnitine into the culture increased colony formation significantly. These results suggest that long-chain acyl carnitine may have an effect on erythropoiesis.