In pot experiments with15N labelled soil and mineral15N, the influence ofBradyrhizobium (Rhizobium japonicum)inoculation and N fertilization on the symbiotic N2fixation and yield of soybeans [Glycine max(L.) Merill., cv. ‘Fiskeby V‘] was investigated. Symbiotic N2fixation only occured after inoculation withBradyrhizobium.Considerable differences in efficiency of the bacterial preparations were observed. Shortly after flowering, the symbiotic nitrogen fixation was finished and, subsequently, soybeans took up considerable N amounts from the soil. N fertilization at seeding suppressed N2fixation of soybeans. In this case, the dry matter and nitrogen yield increased, because the loss of fixed nitrogen was overcompensated by the mineral N uptake. During flowering of soybeans, the N2fixation was not affected by N supply, because this process was already terminated. The mineral N was additionally available to the plants and led to increased N amounts in plants. It was absorbed to a considerable degree by soybeans. The mineral N was translocated (partly, after intermediate storage in the vegetative organs) into the seeds thus increasing their yields.