Several cases of nonfungal microbial disfigurement of exterior paint films on houses and test panels were investigated. The paint films were examined by epifluorescence microscopy techniques and algae and bacteria were cultured from paint film samples. The growth and distribution of algae on surfaces were quantified by measuring in vivo or extracted chlorophyll fluorescence at 680 nm. using a computerized photometer-monochrometer system attached to the microscope. Methods for accelerated laboratory testing of algal and bacterial paint film disfigurement were investigated.