Eucheuma striatum grown in uniculture in natural seawater, at the Department of Marine Resources, Ponape, East Caroline Islands has become subject to disease. Penicillium waksmanii Zaleski was isolated from diseased portions of the alga. This is apparently the first time the fungus has been isolated from a marine source; it will grow on an artificial seawater medium with agar and carrageenan as the only carbon sources.