These findings confirm the opinion that, for exposures
of about 200 mg/m3 or less, individual
hippuric acid concentrations cannot differentiate
occupationally exposed subjects from controls.2' 31 A
good biological indicator must be capable of evaluating
even low exposures, not only in a group of
exposed subjects, but also in individual subjects.
o-Cresol has been suggested as a more specific
biological test of exposure to toluene.'232 Only a very
small proportion ofthe retained toluene is excreted as
o-cresol (