The role of arbuscular mycorrhizas in the transfer of N and P between pea (Pisum sativum L.) and barley (Hordeum vulgare L.) plants was studied in a controlled environment. The plants were grown together in PVC containers, either in symbiosis with Glomus intraradices Schenck and Smith or as non-mycorrhizal controls, and with their root systems separated by an intermediate buffer zone (2 cm), confined by fine nylon mesh. The pea donor plants were supplied simultaneously with N-15 and P-32, using a split-root labelling technique, in order to follow the flow of N and P to the barley receiver plants during 60 d of growth. In half of the containers, the donor-plant shoot was removed 42 d after the start of labelling and the roots were left in the soil to decompose. The reverse transfer of N and P, from barley donor to pea receiver plants was also measured to allow calculation of the net transfer through hyphae between mycorrhizal donor and receiver plants. No significant transfer of N was detected from intact pea donor plants to the barley receiver plants in the non-mycorrhizal controls. Mycorrhizal colonization slightly increased the transfer of N. However, the net transfer of N was almost insignificant since N was also transferred in the reverse direction, from barley to pea. Removal of the pea donor-plant shoots increased the N transfer to 4% of the donor-root N in the non-mycorrhizal controls. Contrastingly, 15% of the donor-root N was transferred to the receiver plants, when plants were colonized by G, intraradices. The results for P transfer followed the same patterns as was observed for N, although in smaller proportions. The results indicate that arbuscular mycorrhizas may play a significant role in the flow of N and P between two plants interconnected by hyphae, when the root system of one of the plants is decomposing.