The cyst wall of Microphallus madrasensis resisted 6 N and 11·3 N hydrochloric acids (HCL) 36 N concentrated sulphuric acid (H2S04) and 0·35 M sodium hypochlorite. It was partially dissolved in 0·6 M sodium azide and completely dissolved in 16 N nitric acid (HNO3). An HCl hydrolysate of the cyst wall contained 10 amino acids viz. alanine, leucine, aspartic acid, glutamic acid, lysine, histidine. phenylalanine. tyrosine. cystine and proline. Polyacrylamide gel electrophoresis revealed the presence of a fast moving fraction which stained with periodic acid-Schiffs (PAS) reagent and toluidine blue was noticed in tris-glycine buffer soluble and methanol water soluble substances present in the cyst wall. Triton X-100 soluble substances present in the cyst wall revealed the presence of two slow-moving fractions stained only with PAS, and also a fast-moving fraction stained only with toluidine blue. Sodium dodecyl sulphate (SDS) soluble substances in the cyst wall revealed the presence of two fast-moving fractions which stained with PAS and toluidine blue. The slow-moving fractions are protein-bound carbohydrates. The fast-moving fractions obtained after fractionation with SDS are acid mucopolysaccharides or nucleoproteins whereas the single fraction (Triton X-100 soluble substances) which stained with toluidine blue appears to be a carbohydrate-free protein. The cyst wall of M. madrasensis also consisted of phospholipids and neutral lipids.