An improved method for diagnosing a disease comprising detecting a disease-specific biochemical marker macromolecule within a sample of extracted cerebral spinal fluid or serum is disclosed. In particular, a radioactively labeled photoaffinity probe is used to diagnose a disease. For instance, Alzheimer\u27s disease can be diagnosed by detecting a disease-specific protein having a molecular weight of about 42,000 daltons, i.e., glutamine synthetase. Also included is a method for detecting other disease states, such as cancer, by detecting the presence or absence of specific nucleotide binding proteins
