Polyamines (putrescine, spermidine, and spermine) are widely distributed in animal and vegetal tissues, where their intracellular concentration strictly correlates with normal and pathological cell growth and protein synthesis. By means of a sensitive HPLC technique, the fasting plasma concentrations of polyamines were measured serially in 11 patients who underwent partial hepatic resection because of focal liver lesions. Samples were obtained before surgery and over the next 6 months, during hepatic regeneration. Liver volume was also measured by ultrasound on the basis of the 3 maximum diameters of the liver. From 2 to 4 weeks after surgery, plasma putrescine increased by a maximum of 78%, and spermidine by approximately 50%. No changes were observed in spermine levels. The spermidine/spermine ratio nearly doubled during liver regeneration. The volume of the liver decrease from 1505 [SD 236] ml to 743 [151] ml after resection, and returned to nearly normal values after 6 months (1231 [100] ml, p < 0.05 vs. basal values). The liver regeneration rate was highest 2-4 weeks after resection, and declined thereafter, when prevailing polyamine concentrations returned to normal. These data show that liver regeneration is accompanied by a significant increase in fasting putrescine and spermidine concentrations, which might be biochemical signals of active liver cell regeneration.