Following a review of selected aspects of fungal macroecology, data are presented about the microecology of Aureobasidium pullulans' growth on an experimental acrylic emulsion paint. When A. pullulans is inoculated onto a virgin film of the coating, an ephemeral period of growth lasting about three weeks precedes dormancy. When the fungus is inoculated onto a film prepared from Pseudomonas-contaminated paint, the fungus continues to grow for at least 10 weeks, at which time monitoring of growth was terminated. Tests in vitro of the ability of A. pullulans to utilize hydroxyethyl cellulose (HEC) as sole carbon source in distilled water were negative, using visible growth of the pigmented mycelium as the criterion. When the 0.5per thousand HEC solution was treated with purified Pseudomonas cellulase prior to inoculation with A. pullulans abundant growth occurred. These data suggest that A. pullulans does not produce HECase when the diluent is distilled water; given the initial digestion of HEC by the supplied cellulose. A. pullulans utilizes the hydrolic products as an energy source for growth. The implications of these findings are discussed in relation to mildew-induced defacement of organic coatings (MIDOC).