The interactions of ten retinoid derivatives with human serum albumin (HSA) and lipoproteins have been investigated in vitro by an erythrocyte-partitioning technique that allows a quantitative estimation of the protein and erythrocyte binding. It was found that all these compounds were highly bound to HSA and lipoprotein. The binding to HSA was superior or similar to the binding to lipoprotein in the case of carboxylic acid derivatives. For the neutral derivatives, the binding to lipoproteins was generally higher than the binding to HSA. Retinoid binding to lipoproteins was strongly related to the computed octanol water partition coefficient (CLOGP).