The pharmacokinetics of a new plasma expander, low molecular weight-hydroxyethyl starch (LMW-HES) were examined in six normovolaemic men. 2. One hour post-infusion, 13.5% of the total dose of LMW-HES injected was excreted in the urine, 50.2% was present in the intravascular space, and 36.3% was unaccounted for. 3. Twenty-four hours post-infusion, 65.5% of the total dose of injected LMW-HES had been excreted in the urine, 4.1% remained intravascularly, and 30.4% was unaccounted for. 4. The plasma volume increased rapidly from a mean value of 45.7 ml kg-1 to a maximum value of 57.9 ml kg-1 immediately post-injection, then gradually returned to normal over 24 h. 5. The infusion of an average of 58.1 g had no effect on ESR, renal and hepatic biochemical indices. 6. LMW-HES appears to be safe and effective, and should be of value clinically when rapid and short-lived augmentation of the plasma volume is required.