Abstract: Antifouling compositions or paints with a high degree of stability and toxic to marine life comprising the combination of (a) cuprous oxide; (b) one or more triorganotin polymer or copolymer carboxylates and (c) at least one relatively inert dehydrating agent of low water solubility which is capable of taking up water either physically or chemically; and optionally also comprising other toxic or non-toxic resin or pigment components, non-aqueous diluents, thinners, extenders or solvents, together with other conventional additives.The component (c) is preferably a relatively inert metal salt of low water solubility, e.g. calcium sulphate in anhydrous or hemi-hydrate form and the polymer or copolymer is generally a substituted or unsubstituted vinyl or acrylic triorganotin polymer or copolymer carboxylate, copolymers being preferred to give the desired choice of physical or mechanical properties.