SUMMARY Lasalocid, a carboxylic ionophore antibiotic, is used frequently in poultry feeds as a coccidiostat, however the present study centered on its role as growth promoter and in steroidogenesis. Twenty turkey poults, 60 days old, were allocated randomly in two equal groups; control group and lasalocid supplemented group (120 ppm). Blood samples were collected at three weeks interval, till the 23rd week, for determination of serum biochemical parameters (glucose, triglycerides cholesterol, total proteins and albumin), and gonadal steroids (namely estradiol and progesterone). Body weight and feed consumption were also determined 274 Assiut Vet. Med. J. Vol. 52 No. 109 April 2006 weekly to calculate feed efficiency. Carcass weight and dressing % were also recorded. The results revealed that lasalocid supplementation did not result in any significant change in glucose, triglycerides and cholesterol concentrations among the two experimental groups, however, the total protein and albumin concentrations were significantly increased in lasalocid supplemented group. Similarly, feed efficiency and dressing % of lasalocid supplemented group were significantly higher than those of the control group. Moreover, serum estradiol (E2) and progesterone (P4) levels were significantly higher in lasalocid supplemented group compared to the control. In conclusion, lasalocid supplementation was found to be useful in terms of increasing feed efficiency in turkey.