The effect of autoclaving soil on vesicular-arbuscular mycorrhizal (VAM) fungal colonization and biomassproduction of tomato (Lycopersicon esculentum Mill.) was assessed in pot experiments under greenhouseconditions. Four treatments were given viz., (1) VAM-free plants in autoclaved soil, (2) VAM plants in autoclaved soil, (3) VAM plants in autoclaved soil amended with VAM-free filtrate of non-autoclaved soil, and(4) VAM plants in non-autoclaved soil. The VAM plants grown in non-autoclaved soil showed the highest root colonization of 87.78% while those under (2) and (3) showed only 55.11 % and 56.94% respectively. On the other hand, significantly higher shoot length (105.4 cm/plant), total leaf area (740.3 cm?/plant) and biomass (8.43 g/plant) were obtained in VAM plants grown in autoclaved soil. VAM-free plants in autoclaved soil had reduced growth. In treatments 3 and 4 plant growth was intermediate. The results indicate that VAMcolonization and sporulation were favoured under natural conditions, but VAM plants under autoclaved soilconditions produced maximum growth.