After a review on studies on membrane structural protein, the purpose of isolating plasma membrane protein in a Neurospora crassa mutant was stated. An aggregate containing protein, lipid and carbohydrate with high content of amino acids with non-polar side chains and low content of aspartate and glutamate has been isolated and studied with gel filtration, electrophoresis and amino acid analysis techniques. It has a molecular weight of about 2,00,000 as estimated by gel filtration. From amino acid analysis, a lipid-carbohydratefree subunit has been calculated to have a molecular weight of 63,500. According to the calculation, the aggregate contained 14 subunits.