ABSTRACT.    This study evaluated the transmission blocking activity of the commercial neem (Azadirachta indica) seed extract Neem Azal^® (NA), as well as the curative activity of NA and of an ethanolic neem leaf extract, using the rodent malaria model Plasmodium berghei / Anopheles stephensi. Infected, gametocytemic BALB/c mice were intraperitoneally treated with NA one hour before the exposure to mosquitoes. The effect on P. berghei ookinete and oocyst development was assessed. NA, containing 34% azadirachtin A and 22% other limonoids, completely blocked the development of P. berghei in the vector: no oocysts were found in mosquitoes (n = 138) fed on mice treated with 50 mg/kg NA, while 91% of control mosquitoes showed 29 (CI95% = 13 - 66) oocysts. Challenging healthy mice by NA 50 mg/kg group mosquitoes didn't lead to blood infection. An interference by NA on ookinete maturation explained the observed inhibition. In the 50 mg/kg NA group, no mature ookinetes were found over 300 microscopic fields (1000x), compared to 13 (CI95% = 7 - 22) in the control mosquitoes. Purified azadirachtin, administrated at the same dose, reduced but did not eliminate mature ookinetes (geometric mean = 3; CI95% = 1 - 7), suggesting that other limonoids present in NA could exert an additive or synergistic effect with it. The curative activity of the extracts was assessed by the Peters 4-day test. Neem leaf extract showed curative activity after oral administration at a dose of 200 mg/kg/day: parasitemia was reduced by 48% (p < 0.002) in respect to control mice. NA, in contrast, did not show any effect on P. berghei blood forms. This lack of curative activity by NA can be explained by the different limonoid composition of the two tested extracts, derived from distinct plant organs. Transmission blocking and curative compounds from A. indica show a high potential for the development of antimalarial drugs and remedies.