Recent advances indicate that cyclic nucleotides and perhaps certain adrenergic metabolites might be directly involved in contact-inhibition mechanisms and tumoral cell growth. CSF levels of 3'-5' cAMP, 3'-5' cGMP, HVA, and 5-HIAA were investigated in patients with supratentorial malignant gliomas, brain stem gliomas and posterior fossa medulloblastoma. cAMP levels were slightly decreased only in medulloblastomas, whereas no significant difference was detectable in patients with supratentorial gliomas. cGMP values turned out to be significantly higher, with a very peculiar increase in the most anaplastic neoplasms. Postoperative follow-up showed a gradual decrease of cGMP values, with progressive restoring of a normal cAMP/cGMP ratio. The possible correlation of these findings with CSF levels of HVA and 5-HIAA is discussed.