A de novo inv dup (15) was diagnosed at amniocentesis. No physical abnormalities were detected after birth. The boy developed severe mental and motor retardation, which became obvious at 16 months of age.

The clinical course of a mannitol intoxication in a 5-month-old infant is reported. Mannitol measurements were performed by gas-chromatographic-mass-spectrometric analysis. The role of the osmolal gap as a simple diagnostic tool in mannitol intoxication was underlined by comparison to serum mannitol levels. Mannitol elimination was analysed by measuring mannitol levels in urine, ultrafiltrate, and peritoneal dialysis outflow. The highest concentrations were found in urine (approx. 300% serum values) and the lowest in peritoneal dialysis outflow (approx. 50% serum levels). "Total body Mannitol" was calculated each day from body weight, hydration, and serum mannitol levels and opposed to the amount eliminated via urine, ultrafiltration, and peritoneal dialysis. The results were only compatible with a volume of distribution of approx. 5.3 1, representing total body water at a lean body weight of 7 kg. It could thus be demonstrated that the sudden fall of serum mannitol levels from 19.6 mg/ml to 5.5 mg/ml without dialysis treatment in an anuric patient was due to a leak of mannitol into the intracellular compartment.