The objective of this study was to compare the interaction between Frankia and vesicular-arbuscular mycorrhizae (VAM) on the growth response of Alnus acwninata H.B.K. seedlings under three different phosphorus levels. Alnus acuminata seedlings grown in sterile vermiculite, were inoculated with Frankia strain HFPArI3 and/or VAM (as Glomus inwa-radices) under three phosphorus levels (10.50 and 100 pg g'). After 120 days diiferences in growth were observed at the 50 pg g" P level between nodulated and non-nodulated plants; whether inoculated with Frankia + VAM or just with VAM. Interaction between Frankia and VAM was positive with respect to nodule weight at 50 pg g7' P level. The data suggest that the presence of VAM can compete with the nodules as a carbohydrate sink. At increasing levels of P the presence of Frankia alone statistically increased growth over that of the control.