In homogenates of corpus striatum from rats, incubated in the presence of adenosine triphosphate (2 mM) (45 min, 37 degrees C), a loss (approx. 50%) of muscarinic cholinergic binding sites could be detected using a 3H-3-Quinuclidinyl benzilate (3H-3-QNB) binding assay. We found that only vanadium-contaminated ATP induced loss of muscarinic binding sites. Orthovanadate (1 mM) alone in the absence of ATP induced loss (approx. 60%) of binding sites just as "vanadium-ATP" did.