Incubation of ciliates, with fungal zoospores in the presence of three antibiotics resulted in a continuous increase in concentration of volatile fatty acids (VFA) from about 930 mM/100 ml at the start of incubation to over 1010 mM/100 ml after 12 h (P < 0.05). The concentration of VFA in control cultures incubated without substrate (Fig. 2) increased to only 960 mM/100 ml (P < 0.05) The similar effect was observed in cultures incubated with and without commercial chitin [23]. No changes were found in the concentration of VFA in the absence of protozoa (bacterial control).