The root-nodule bacteria, Rhizobium spp, in a symbiotic relationship with leguminous plants, make an important contribution to nitrogen input in soils. For this reason most research on rhizobia has as its aim a better understanding of the symbiotic nitrogen fixation carried out by rhizobia, and the agricultural benefits of this process. Rhizobial nitrate reduction and denitrification (Rajagopalan, 1938; Ishizawa, 1939; Lepidi and Picci, 1967) have been known for some time, but only recently has it been conclusively demonstrated that many strains of rhizobia denitrify (Zablotowicz et al., 1978; Daniel et al., 1980b, 1982) and are capable of removing fixed nitrogen from soils (Daniel et al., 1980a; O’Hara et al., 19E4). Our purpose is to review progress made in the study of rhizobial denitrification and to discuss recent results in relation to the important role of rhizobia in agriculture.