The interference of eight components in the yield of sporulation and thermal resistance to moist heat (121degreesC) of Bacillus stearothermophilus spores suspended in 0.02 M calcium acetate solution and inoculated on paper strips previously treated with calcium acetate/calcium hydroxide was studied. The spore yield of 1.0 x 10(8)/mL was developed at 62degreesC in 17 media containing different concentrations Of D-glucose, sodium chloride, L-glutamic acid, yeast extract, peptone, manganese sulfate, potassium phosphate, and ammonium phosphate. The combined effects of yeast extract, peptone, and glucose contributed positively to the spore yield and to the stability of the thermal resistance of both spores in suspension and on strips.