N-De-ethylation of atrazine occurred in cell-free extracts of the white rot fungus, Pleurotus pulmonarius, after incubation of 6-day old mycelium with 0.1-1 mM Mn2+. De-ethylatrazine was confirmed by TLC, GC and by MS. The rate of N-de-ethylatrazine production increased from 0.07 to 0.31 mu mol/mg protein in a 7 h reaction when mycelium were pre-incubated with Mn2+ for 5 and 24 h, respectively. An unidentified, de-chlorinated metabolite was also produced, unrelated to conditions of incubation with Mn2-.