Abstract. The magnetic properties of the reduced catalase from Lactobacillus plantarum have been studied for the active enzyme and its fluoride complex through variable field/variable temperature magnetization measurements. The magnetic exchange interaction deduced from these experiments [fluoride complex: J=1.3(1)cm1; active enzyme: J=5.6(5)cm1; H=2JS1S2] are similar to those presently obtained in a re-analysis of the data for the corresponding forms of the Thermus thermophilus enzyme (previously published in 1997, Angew Chem Int Ed Engl 36:16261628): phosphate complex: J=2.1(2)cm1; active enzyme J=5.0(3)cm1. These results concur to a unified picture for the two enzymes, consistent with the presence of a hydroxide bridge in the reduced active catalases and its replacement by an aqua bridge in the anion-inhibited enzymes as the main mediators of the magnetic exchange.