The heat resistance of spores of Bacillus coagulana strain Sp. 33, isolated from canned chopped spinach, has been determined. It appeared to be higher in 1/40 M phosphate than in 1/16 M phosphate and higher at pH 6.8 than at pH 6.0. In 1/40 M phosphate buffer of pH 6.8 the calculated D,,, was 2.4 min. In chopped spinach of pH 6.2 the calculated D1,, was 0.84 min. In addition a simple and reliable method of assessing the thermal resistance of micro-organisms in thermal death time tubes is reported.