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Some properties of cathepsin B and a-N-benzoylarginine-~- naphthylamide (BANA) hydrolase from bovine lymph nodes have been studies. a-N-benzoylarginine-~-naphthylamide was a sensitive substrate for both enzymes. Leucine-2-naphthylamide was cleaved only by BANA hydrolase. Degradation of low molecular weight substrates was optimal at pH = 6.0. At this pH value, the enzymes were most stable. Cathepsin B inactivated aldolase, was inhibited by 1 μM leupeptin and by thiol blocking compounds. BANA hydrolase was not inhibited by 1 μM leupeptin but showed that it required thiol compounds and EDTA for full activation. It was concluded that BANA hydrolase is very similar or identical to cathepsin H from rat liver lysosomes.