The concentration of myo-inositol in samples of human blood serum and plasma, cerebrospinal fluid, and seminal fluid, were determined by gas chromatography of the trimethylsilyl derivative. The average inositol level in blood serum was 6.9 μg/ml. Higher values were found in pools of serum obtained from a mixed patient population from a general hospital. High inositol values were found in pooled plasma from uremic patients. Patients with depression did not demonstrate significant differences from normal controls, whether or not they were treated with lithium carbonate. A survey of cerebrospinal fluids from a patient population revealed inositol values from 4-163 μg/ml, with the majority of samples falling between 6 and 35 μg/ml. In a few samples extremely high values were found. Clinical findings and discussion of these cases are included.