Trials were replicated in an aerated reactor vessel to obtain quantitative data on the relationships between aeration, temperature, and performance of municipal sludge composting. Temperature, airflow, and carbon dioxide evolution were monitored continuously in sections (6.1 by 3 m deep) of the reactor. Aeration was regulated by temperature feedback to maintain sections of the reactor at widely different temperatures. Rates of drying and volatile solids destruction were considerably higher at mean temperatures of 40 degrees to 60 degrees C than at temperatures above 60 degrees C. Carbon dioxide evolution rates comparable to those reported for laboratory composting trials indicated optimal microbial activity at mean temperatures between 40 and 60 C. High temperatures for pathogen destruction were achieved readily toward the end of the process by airflow reduction or reversal.