A critical concentrationC*is identified at which interaction or overlapping of the domains of polymer molecules in solution first occurs. Thirty-three experimental values ofC*from eight different systems, drawn from 10 literature sources and using seven different detection procedures, were correlated with an average absolute deviation of 22.1%. The correlation is particularly useful because, in contrast to other procedures, it requires no physical measurements and involves a new application of molal volume estimates from standard tabulations. Extension of the study to wider ranges of polymer and solvent types is advocated.