Summary Photaffinity labelling (PAL) with [32P]8-azido-cAMP and polyacrylamide gel electrophoresis (PAGE) has been used to identify three specific cAMP-binding proteins (cAMP-BPs) within cytosols derived from the centre and periphery of 32 human colorectal cancers and from related adjacent (less than 5 cm from the tumour) and distant (more than 5 cm from the tumour) microscopically benign mucosa. By immunoprecipitation with specific anti-RI and anti-RII antibodies these proteins have subsequently been characterised as a single form of RI (48 kDa