Microbiological analysis of spoiled paints and raw materials has always been performed aerobically. However, when examined under anaerobic conditions, 11.8% of paints, 6.4% of latexes, and 2.4% of pigment slurries are found to contain anaerobic bacteria. Among all microbially contaminated materials, 27% contained anaerobes. The organisms found are primarily from the genera <i>Clostridium</i> and <i>Bacteroides</i>. Pure cultures of these organisms are shown to degrade water-based paint ingredients, e.g., hydroxyethyl cellulose, surfactants, glycols, etc. Facultative anaerobes also present in contaminated materials show different effects under aerobic and anaerobic conditions. Mixtures of obligate anaerobes and/or facultative anaerobes were active in causing a loss of paint viscosity, malodors, and discoloration. These results suggest most paint spoilage occurs under anaerobic conditions.