Tear prealbumin previously isolated from the saline-extractable human ocular mucus was further examined for microheterogeneities using crossed-iirmunoelectrophoresis through development with antiserum to the isolate. The isolate was examined following the final two stages of its chromatographic purification by DEAE ion exchange and Sephadex G-75. The crossed-immunoelectrophoretic pattern of the tear prealbumin isolate, recovered following DEAE ion exchange chromatography, indicated the existence of two types of minor degrees of binding between tear prealbumin and serum albumin. One type appeared to be tightly associated while the other was interpreted as weakly bound, where serum albumin was separable from tear prealbumin in an electric field. The total association of serum albumin with tear prealbumin in this isolate was estimated to be about 3–7%. Crossed immunoelectrophoresis of the isolate after its final stage of purification on Sephadex G-75 chromatography showed the absence of the weakly bound serum albumin. Hawever, the tight tear prealbumin/serum albumin association remained, estimated to be 1–3%.