Abstract: An oral preparation for reduction of mammalian, e.g. human, cat or dog, plaque and/or calculus, such as bacterial plaque, arteriosclerotic plaque, atherosclerotic plaque, pleural plaque, dental calculus, renal calculus, biliary calculus, and prostatic calculus, contains a Ascophyllum sp., especially A. nodosum, seaweed or an extract thereof. The oral preperation is suitable for use in prophylactic and/or therapeutic method of treating plaque and/or calculus in a mammalian individual.