Two situations required a modified determination of coenzyme Q10 (CoQ10) in human blood and organ tissue. Blood from patients with AIDS and cancer raised apprehensions about safety to an analyst, and the number of specimens for analysis is increasing enormously. A modified determination replaces silica gel-TLC with disposable Florisil columns, and steps were simplified to allow more analyses per unit time. Data from the modified determination are quantitatively compatible with data from older and tedious procedures. This determination was used for blood from 36 diverse patients with allergies. The mean CoQ10 blood level of these patients is not different from the mean level of so-called normal individuals, but approximately 40% (14/36) of these allergic patients had levels up to 0.65 micrograms/ml, which is the level of dying class IV cardiac patients. The biosynthesis of CoQ10 in human tissues is a complex process that requires several vitamins and micronutrients, so that countless vitamin-unsupplemented Americans may be deficient in CoQ10. The relationship of allergies to autoimmune mechanisms and immunity, and the established relationship of CoQ10 to immune states, may be a rationale for therapeutic trials of administering CoQ10 to patients with allergies who have low CoQ10 blood levels and are very likely deficient.