In our study of 262 hospitalized flame burn patients, serum hyperosmolality, defined as having at least two reported osmolality values greater than 310 mOsm/kg, was observed in 15 patients (6%). From this group, nine patients were found to have an osmolal discrepancy (reported serum osmolality minus calculated serum osmolality). All patients in this group had a burn surface area greater than 35% TBS. The discrepancy between reported osmolality values of two patients from this group, determined by freezing point depression and vapor point analysis, suggested that a volatile substance was contributing to the osmolality. Further analysis by gas chromatography revealed propylene glycol as the agent accounting for most of the osmolal discrepancy. The only exposure to this polyalcohol was from the topical antibiotic cream (silver sulfadiazine) used in their treatment.