1. 1. The metabolism of inositol (Ins)-containing phospholipids and inositol phosphates has been studied by following the incorporation and distribution of myo-[3 H]Ins in metabolically active electrocytes from the electric ray Discopyge tschudii. 2. 2. The apparent initial rate of myo-[3H]Ins incorporation into total phosphoinositides was ca 8.2 fmol/mg protein/hr. Phosphatidylinositol (Ptdlns) displayed the highest levels of labelling. Lithium inhibited this incorporation probably by limiting the recycling of myo-[3H]Ins from [3H]Ins-monophosphate. 3. 3. The formation of water-soluble products of phosphoinositides between 7 and 24 hr was 4.1 ± 0.2, 0.4 ± 0.2 and 3.0 ± 1.0 fmol/μmmol total lipid phosphorus for myo-[3H]InsP, -InsP2 and Ins-P3 respectively. 4. 4. Lithium ions are shown to modulate phosphoinositide synthesis and Ins-phosphate accumulation. Ins-mono-, bis- and tris-phosphate production was enhanced 5-, 3- and 2-fold by Li +. 5. 5. The above results suggest the participation of a C-type phospholipase and of Li-sensitive phosphatases in the modulation of phosphoinositide metabolism in the electrocyte.