The capacity of 9 biochemicals to interfere with gas chromatographic exclusion screening analyses for volatile agents encountered in forensic blood samples was studied. The chloroform extractabilities and gas chromatographic retentions on OV‐17 (at 160° column temperature) of 9 biochemicals were examined. On direct chloroform extracts of blood, gas chromatographic peaks were obtained with indole, 2‐phenylethylamine and β‐hydroxybutyric acid. No gas chromatographic peaks were obtained with glycine, cholesterol, cortisol, urea, tyramine and stearic acid. The retention distance of these three biochemicals interfered with the retention distance of the volatile drugs i. e. methyl salicylate, terpin hydrate, phenyl salicylate, amphetamine, acetanilide, and ca