The host specificity, infection process and effectiveness of nodules produced by several African sinorhizobial strains on different Acacia and Prosopis species (Leguminosae, Mimosoideae) were studied. Sinorhizobium arboris strain HAMBI 1552T, S. kostiense strains HAMBI 1489T and HAMBI 1493, S. saheli strain HAMBI 1496 and S. terangae bv. acaciae strain ORS 1058 induced nitrogen fixing nodules on seedlings of the following African or Latin American species (marked with *): A. angustissima*, A. mellifera, A. nilotica, A. oerfota (synonym A. nubica), A. senegal, A. seyal, A. sieberiana, A. tortilis subsp. raddiana, P. chilensis*, P. cineraria, P. juliflora and P. pallida*. All strains increased plant yield significantly compared with uninoculated seedlings watered with nitrogen-free medium, but none appeared to be superior. The sinorhizobial strains were unable to effectively nodulate Sesbania rostrata (Papilionoideae).