Abstract: Compositions for delivering release materials, for example drugs, agricultural materials, other bioactive materials, cosmetic materials, organic or inorganic compounds which take part in or catalyse a chemical reaction, a fragrance-emitting material for a vaporizer, or a lubricating material. The release material is associated with a crystalline carrier. The carrier may be a crystalline polymer containing a plurality of crystalline groups or a crystalline monomer which contains a single crystalline group, the crystalline group preferably comprising a straight chain polymethylene radical containing at least 16 carbon atoms. Some of the carriers are obtained by modifying hyaluronic acid, collagen, gelatin, a polysaccharide, a carbohydrate or cyclodextran. The release material may contain a similar crystalline group, for example may be an active compound which has been modified to introduce a crystalline group.