Phosphorus and zinc were determined microbiologically using an AspergilIus niger strain isolated from a volcanic-ash derived soil. This strain gave the highest response both to P and Zn when compared with 48 other fungu's strains isolated from 8 different volcanic-ash derivedsoils.
Techniques based on the dry weight of the mycellium of the fungus grown in the presence of soil for 7 days at 28°C were used, and campared withstandards set up for each element. Growth response to P was very high and up to 30% of the total P was accounted for. Results for Zn were of the same arder of magmtude than the one extracted by 0.1 M HCl, and correlated significantly with it (r=0,79).