ethane production from a high-solids digester was significantly decreased by both feedstock starvation and overfeeding. Both starvation and overfeeding also induced significant decreases in acetate turnover, acetate incorporation into methane, and in the ratio of triglyceride to polar lipid. The physiological status ratio of %acetate incorporated into poly-b-hydroxybutyrate to polar lipid was unchanged by either treatment. Digester pH, and acetate and ammonia concentrations were unchanged by starvation, Overfeeding decreased the pH, and greatly increased ammonia and acetate, creating a toxic environment. The rate of ‘%Z-acetate incorporation into total lipid significantly increased with starvation but significantly decreased with overfeeding. The ratio of %-acetate incorporated into eubacterial and eukaryotic fatty acids to methanogen ether lipids significantly increased with starvation and significantly decreased under overfeeding. This study provides one of the most thorough descriptions currently available for starvation and overfeeding stress effects on methanogenic digester performance, including specific eubacterial and archaebacterial activities. These results provide important insight into methanogenic digester operating parameters for stable biomass-to-methane yields.