Endogeic earthworms Pontoscolex corelhrurus were inoculated at four different biomasses (i.e. 0, 100, 400 and 800 mg/1.5 kg dry soil) in pots containing seedlings of three tropical fruit trees: Bactris gasipaes (peach palm), Bixa orellana and Eugenia stipitata. After 120 days, significant increases of plant growth were observed in Bixa (14-24 times the control value) and Eugenia (1.6-2.5) as a result of earthworm inoculation irrespective of the inoculated biomass; an inverse effect (-1.8 to -2.7 times the control) was observed with seedlings of Bactris. There was a significant effect of plant species on earthworm growth and significant effects of earthworms on mineralization of nitrogen and microbial biomass accumulation at some dates. Different conditions in the rhizosphere of these species may explain these results. Kinetics of soil variables during the experiment were complex. It is suggested that in some pots an excessive earthworm activity resulted in the sealing of surface with compact casts and further changes in water dynamics which affected both earthworms and microbial communities. © 1992.