Abstract Haptoglobin was detected more readily in starch gel electrophoresis of C.S.F. concentrates from individuals of haptoglobin type 1-1 than from those of types 2−1 and 2-2. The haptoglobin pattern was the same as that observed in serum in type 1-1 but in types 2−1 and 2-2 the proportion of the different bands was changed as there was relatively more of the faster moving and presumably lower molecular weight components. If the haptoglobin in C.S.F. is derived from serum these results suggest that the lower molecular weight haptoglobin components gain entry into the C.S.F. relatively more easily than those of higher molecular weight.