A study was conducted to evaluate the effect of 3 different levels (1.25, 2.5 or 5.0%) of black cumin seeds (BCS) on five hundred chicks. A basal diet was supplemented with either 0 (negative control), or 0.1% antibiotic (positive control), or 3 levels of BCS. At day 28 and 42 of age, the 2.5 and 5.0% BCS groups had significantly greater body weight gain (BWG) than the 1.25% BCS and the antibiotic group. The same groups had feed efficiency significantly improved (P<0.05) compared to the 1.25% BCS group and the controls. At both ages, measurement of the dressing percentage showed no marked variation between BCS supplementation and antibiotic. The 2.5 and 5.0% BCS groups showed an increase (P<0.05) in total protein and higher (P<0.05) haematological values than the 1.25%, antibiotic or unsupplemented diet group. The activities of blood enzymes were lower (P<0.05) and caecal coliform and Escherichia coli populations decreased (P<0.05) in BCS and antibiotic groups. Serum and tissue cholesterol concentration decreased (P<0.05) as the levels of BCS increased. The geometric means haemagglutination inhibition (HI) titres of the BCS and the antibiotic group were always higher than the negative control. The mean lymphoid organs weight/body weight ratio of the negative control was significantly (P<0.05) lower than BCS and antibiotic groups. In conclusion, including up to 2.5 or 5.0% BSC in the diets of broilers has no deleterious effects on their performance, immunity, serum biochemical constituents nor haematological indices. In fact, it may lead to the development of low-cholesterol chicken meat.