About two hundred and fifty urine samples were collected some years ago in the course of experimental exposure of one individual to benzene vapor. Phenol concentrations and specific gravities were recorded, together with the volume of urine samples and the times of voiding. Review of this data shows that the reciprocal of specific gravity minus unity (SG 1) measured by refractometer correlated closely with urinary flow rate, while those using the traditional urinometer correlated much less closely. If this is valid for all workers, then refractometer measurement of specific gravity may be used as a surrogate for flow rate. More consistent interpretation of spot urine sampling results as a measure of intake of hazardous substances through occupational exposure is then possible. This is particularly the case if used in conjunction with the formula developed and tested by Araki et al. for flow rate adjustment.