The report gives results of research to characterize the anaerobic biodegradability of the major biodegradable components of municipal solid waste (MSW). Measured methane (CH4) yields for grass, leaves, branches, food waste, coated paper, old newsprint, old corrugated containers, and office paper were 144.4, 30.6, 62.6, 300.7, 84.4, 74.3, 152,3, and 217.3 mL CH4/dry g, respectively. While there was a general trend of increasing CH4 yield with increasing cellulose plus hemicellulose (carbonhydrate) content, many confounding factors precluded establishment of a quantitative relationship. Similarly, the degree of lignification of a particular component was not a good predictor of the extent of biodegradation. In parallel with the decomposition experiments, leachate from the decomposition of each refuse constituent was analyzed for toxicity using a modified anaerobic toxicity assay. Leachate toxicity was not found in association with the decomposition of any refuse component other than food waste. However, substantial toxicity was measured in leachate from the food waste reactors. The toxicity was consistent with the behavior of the reactors but could not be simulated with high concentrations of carboxylic acids and sodium.