A study of the effects of iron dextran supplementation on anaemia in indoor lambs was carried out on one commercial flock of 525 lambs from January to June 1993. The lambs were randomly allocated into two groups, one of which was given a parenteral injection of 300 mg iron dextran and the other was left untreated. Blood was collected from 22 12-dayold lambs and 106 24-day-old lambs, in each case half treated and half untreated. The supplemented lambs had significantly improved haematological values than the unsupplemented lambs. There were also significant differences i'n the total serum iron concentration, the unsaturated iron binding capacity and the percentage serum saturation with iron between the treated and untreated lambs. At 12 days, the untreated lambs had a total serum iron below the accepted normal range for sheep whereas the treated lambs had values within the normal range. At weaning, lambs injected with iron dextran were significantly heavier (1.0 kg) than those not injected. The daily liveweight gain to slaughter was greater and the proportion of deaths was lower in the treated lambs but these differences were not statistically significant.