Malaria is highly endemic and unstable in the central Highlands plateau of Madagascar. The infection is seasonally transmitted by Anopheles funestus and An. arabiensis. The latter species is abundant especially in rice-growing areas. The field efficacies of commercial formulations of Bacillus thuringiensis H-14 and B. sphaericus (strain 2362) were assessed against An. arabiensis in 5 types of larval habitats. The granular formulation of B. thuringiensis (Vectobac GR) provided very good control in small ponds and rainwater ditches. In ricefields complete larval control was achieved with Vectobac GR and the flowable concentrate (Vectobac 12AS) at 2.5 kg/ha and 0.6 liter/ha, respectively. The granular formulation of B. sphaericus (ABG 6185) showed activity similar to that of Vectobac GR in small pools and ricefields. ABG 6185 was less effective in rainwater ditches where it gave satisfactory control at rates not lower than 6 kg/ha.