LACTOBACILLI are considered to be catalase-negative1, or occasionally to produce very small amounts of catalase2. The lactobacilli isolated from dairy products have always been found to be catalase-negative3,4. During recent work on the microflora of Cheddar cheese, we have encountered strains of lactobacilli which possess both strong and weak catalase activity. Three strains of Lactobacillus plantarum, originally isolated by Sherwood3 from New Zealand Cheddar cheese, were found to be catalase-positive. Two of the strains gave strong catalase reactions whereas the other strain was much weaker (see Table 1). Serological5 and physiological6 tests have shown that these latter organisms are typical strains of L. plantarum.