Five local and seven standard strains of Rhizobium cicer were compared in terms of their efficiency in increasing the nitrogen content of the chickpea. Shoot dry weight, nodule number, nodule dry weight, protein and total nitrogen contents were taken as the parameters of plant productivity. Different combinations of the strains that were found to be promising (385, 620, Y-29 and 3379) were next employed. The maximum increase in total nitrogen content was only 3.5-fold in single infection whereas an increase as great as 35-fold was recorded for multiple infections. The double infection with Y-29 and 385 as well as the triple infection with Y-29, 620 and 3379 gave rise to the maximum values. Competitiveness of the strains in mixed infections was determined through their recovery from root surfaces and nodules and their subsequent identification. The: effects of soil pH and of varying the concentration of some minerals on the outcome of symbiosis were also reported. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.