After in vivo radiolabeling of Ehrlich cells for 24h with conventional myo-[2- 3 H]inositol we previously demonstrated an aberrant 3 H-labeling of ATP that interfered in the HPLC analysis of inositol trisphosphates. This aberrant 3 H-labeling was accounted for by the extensive kidney catabolism of myo-[2- 3 H] inositol with delivery of 3 H-labeled metabolites to extrarenal tissues. As expected, the aberrant labeling of ATP is markedly reduced with the use of 3 H-myo-inositol labeled at L-C1 rather than at C2, reflecting that the 3 H at L-C1 disappears in the first step of the myo-inositol catabolism: the oxidative conversion to d-glucuronate. In contrast, with the 3 H at C2 of myo-inositol, the 3 H-C2 passes into the pentose phosphate conversions with resulting labeling of nucleotides. The extent of catabolism to 3 H-labeled water, the cellular accumulation of 3 H-myo-inositol, the incorporation into cellular inositol phospholipids, and the labeling pattern of cellular phosphoinositides were all found to be similar for the two labeled myo-inositol moieties. With the use of l-myo-[1- 3 H]inositol an aberrant 3 H-labeling at about 25% remained, for which a presumptive mechanism is proposed. l-myo-[1- 3 H]Inositol appears nevertheless to be a preferable alternative to myo-[2- 3 H]inositol for tracing the intact myo-inositol molecule after in vivo labeling, with minimized interference from aberrant 3 H-labeling of nucleotides.