Thermoactinomyces thalpophilus produced a raw-starch digesting amylase (RSDA) when grown on both cereal and tuber starches. Glucose, maltose and glycerol repressed enzyme production. Highest activity was recorded on rice starch (39 U ml(-1)). Considerable variability existed in the effectiveness of nitrogenous nutrients to stimulate expression of RSDA. Multiple pH optima for RSDA production and activity suggests enzyme heterogeneity.