The ecophysiological variabilities in the ectohydrolytic enzyme profiles of the three species of Pseudoalteromonas, P. citrea, P. issachenkonii, and P. nigrifaciens, have been investigated. Forty-one bacteria isolated from several invertebrates, macroalgae, sea grass, and the surrounding water exhibited different patterns of hydrolytic enzyme activities measured as the hydrolysis of either native biopolymers or fluorogenic substrates. The activities of the following enzymes were assayed: proteinase, tyrosinase, lipase, amylase, chitinase, agarase, fucoidan hydrolase, laminaranase, alginase, pustulanase, cellulase, P-glucosidase, alpha- and beta-galactosidases, beta-N-acetylglucosaminidase, P-glucosaminidase, P-xylosidase, and alpha-mannosidase. The occurrence and cell-specific activities of all enzymes varied over a broad range (from 0 to 44 mumol EU per hour) and depended not only on taxonomic affiliation of the strain, but also on the source/place of its isolation. This suggests 'specialization' of different species for different types of polymeric substrates as, for example, all strains of P. citrea and P. issachenkonii hydrolyzed alginate and laminaran, while strains of P. nigrifaciens were lacking the ability to hydrolyze most of the algal poly saccharides. The incidence of certain enzymes such as fucoidan hydrolases, alginate lyases, agarases, and alpha-galactosidases might be strain specific and reflect its particular ecological habitat.