Population dynamics of legumes and their associated rhizobia were determined in kikuyugrass (Pennisetum clandestinum Hochst. ex Choiv.) pastures at four sites on the island of Maui, Hawaii, USA. Ranges in factors measured at the sites which represented three soil great-groups were mean annual rainfall (MAR) 810-1800 mm yr-1, pH 5.0-6.5 and total extractable bases 3.7-54 mEq 100 g-1 soil. Competition from kikuyugrass, as estimated by mat thickness of the stolons, significantly reduced the abundance of white clover (Trifolium repens L.) but not that of Desmodium intortum cv. Greenleaf (Mill.) Fawc. and Rendle. Soil populations of Rhizobium leguminosarum bv. trifolii and Bradyrhizobium sp. ranged l.7S-5.49 (log10 g-1 soil) and were significantly correlated with increased host legume presence but not with soil pH, total extractable bases (mEq 100 g-1 soil) or MAR.