[en] Biomass of 4-year old trees alphonso mango was estimated by injecting of carrier-free ³²P into the trunk followed by radio-assay of the isotope after a complete dilution of ³²P in the tree, being 3 months after injection. The isotopically calculated plant volume (59 903-68 981 cc plant^-1) and biomass (31.70 - 36.23 kg plant^-1) showed good agreement but generally overestimated both by about 23% compared to the actual values determined physically (43 720-60 693 cc plant^-1 and 22.88-34.78 kg plant^-1, respectively). Application of the technique in a set of another four 15-year old mango trees yielded volume estimates of 1, 70, 749-1 75 835 cc plant^-1 (mean=1, 75 835±1.12%) and biomass estimates of 73.0 - 87.4 kg plant^-1 (mean=80.45±6.8%). The technique is of promise in fertilizer use efficiency and nutrient dynamics studies in tree crops. (author)