The concentrations in selected breakfast cereals of inositol tris-. tetra-. penta-. and hexakisphosphate (IP3. IP4, IP5, IP6) were determined by HPLC methodology. In addition, the calcium. magnesium, and zinc concentrations were determined by atomic absorption spectrometry. All cereals examined contained each of the inositol phosphate (IP) species. Wheat and oat cereals contained an overall average of 5 and (8 \mu \mathrm{mol} / \mathrm{g}), respectively, of IP6, representing 46 and (65 %) of total IP. The mean IP6 content of bran or bran added cercals was (13 \mu \mathrm{mol} / \mathrm{g}). (65 %) of the total IP content. Corn. rice. and most multigrain-based cereals contained lower concentrations of IPs. Whole grain or bran cercals to which no source of (\mathrm{Ca}) or (\mathrm{Zn}) was added averaged (10.9 \mu \mathrm{mol}(0.44) (\mathrm{mg}) / \mathrm{g}) of Ca. (0.48 \mu \mathrm{mol}(0.032 \mathrm{mg}) / \mathrm{g}) of (\mathrm{Zn}). and (57.1 \mu \mathrm{mol}(1.4 \mathrm{mg}) / \mathrm{g}) of (\mathrm{Mg}). Corn and rice cereals contained lower amounts of (\mathrm{Ca}, \mathrm{Zn}), and (\mathrm{Mg}). Calculated indices of bioavailability, such as phytate/Zn and phytate/Ca molar ratios are most meaningful if based on values for IP6 or IP6 + IP5 rather than total IPs. &c 1995 Academic Press, Inc.