Protein and calorie malnutrition is common in chronic dialysis patients. Several interventions have been proposed to prevent and/or to treat malnutrition including the use of recombinant human growth hormone (rhGH) as an anabolic agent. We have previously reported a significant decrease in net urea nitrogen appearance along with modest but statistically significant decrements in several blood chemistries including serum potassium, phosphorus, albumin and a small increase in creatinine concentration during rhGH administration in CAPD patients. In order to evaluate the underlying mechanism of these changes, we systematically evaluated the plasma and dialysate amino acid profiles in blood and dialysate samples of the same patients during their participation in the study. The design of the study was prospective, cross-over with the patients serving as their own controls. There were three study periods: baseline (preGH), treatment (Tx), and follow-up (PostGH). During the seven days Tx period, patients self-administered 5 mg/day s.c of rhGH. Compared to PreGH period, administration of rhGH resulted in a significant decrease in essential amino acids (EAA), in both plasma (935 +/- 243 mumol/liter vs. 801 +/- 186 mumol/liter; P < 0.05) and dialysate (623 +/- 244 mumol/liter vs. 415 +/- 122 mumol/liter; P < 0.05). This decrease was evident in 8 out of 10 individual EAA, and the extent of decrease ranged from 15% to 28% for plasma EAA and from 30% to 45% for dialysate EAA. On the other hand, plasma non-essential AA levels increased significantly during treatment (2537 +/- 776 mumol/liter vs. 3177 +/- 1259 mumol/liter; P < 0.05). All changes returned to baseline values after discontinuation of rhGH. Our findings suggest that the net anabolic processes induced by rhGH reflect a shift in AA metabolism towards peripheral muscle tissues.