Nonporous polyurethane membranes were synthesized using toluene 2,4-diisocyanate (TDI), polypropylene glycol (PPG), or polytetramethylene glycol (PTMG) as polyols and 1,4-butanediol as chain extender. The percentage of hard segments was varied keeping the NCO/OH ratio constant as 1. 1. The permeation of glucose, albumin, and insulin through these membranes was studied using spectrophotometric assays. The permeation of glucose was found to be dependent on the hard segment content and hydrophobicity of the polyols, whereas insulin permeation was found to vary with the hydrogen bonding and hard segment content. The permeation of albumin was almost negligible in both systems. As the synthesized nonporous polyurethanes allow the transport of the nutrients＇ glucose and insulin and prevent the transport of albumin with a molecular weight of 60,000 and immunoglobulins with a molecular weight of 150,000, the membranes are proposed as potential encapsulation matrices for the immunoisolation of islet cells.