The effect of alaproclate in carbachol-stimulated inositol phospholipid (PI) breakdown in rat cerebral cortical miniprisms has been investigated. Carbachol-stimulated PI breakdown was greatly enhanced by increasing the assay potassium concentration from 5.88 to 18.2 mM. Alaproclate, on the other hand, did not influence carbachol-stimulated PI breakdown over the concentration range tested (0-100 microM) at either assay [K+]. The elution pattern of the inositol phosphates from the Dowex-1 columns was also unaffected by alaproclate both in the absence and presence of carbachol. Thus, the potentiation by alaproclate of tremor and salivation induced by the muscarinic agonist oxotremorine in-vivo reported previously is not seen when muscarinic function is measured in-vitro using carbachol-stimulated PI breakdown.