NEW MATERIAL:The novel cholic acid derivative of formula I [R1 and R2 are H or OH (when R1 is OH and R2 is H, the steric configuration may be α or β; when both R1 and R2 are OH, it is α; and when R2 is OH, it is always α); R is group of formula II (n is 2 or 3) or formula III (X is OH, -NHCH2COOH, or -NHCH2SO3H)].

EXAMPLE: Glycolithocholic acid 3-(o-maleimido)benzoate.

USE: Useful as a hapten for radioimmunoassay. An antibody having high specificity can be prepared therefrom.

PROCESS: The compound of formula I (R is group of formula II) can be prepared e.g. by (1) reacting the cholic acid (derivative) of formula IV (X' is X or a group convertible to X by hydrolysis) with succinic anhydride or glutaric anhydride, (2) reacting the resultant 3-hemisuccinoyl- or 3-hemiglutaroylcholic acid derivative with N-hydroxysuccinimide, and (3) when X' is other than X, hydrolyzing the reaction product.