The objective of this study was to compare the nutritional value of three parenteral fluids: a conventional solution (400 milliosmoles/liter, containing Na, K, and Cl in 5% glucose); the concentrated hyperalimentation solution of Dudrick (1,800 milliosmoles/liter, containing Na, K, Cl, Mg, Ca, P, and amino acids in 20% glucose); and an experimental solution (900 millisomoles/liter, containing Na, K, Cl, Mg, Ca, P, and amino acids in 6.5% glucose). These three solutions are termed P400, C1,800, and P900, respectively. Preliminary studies showed that when 5 mg of cortisol/liter were added to P900, this fluid could be infused through peripheral veins for as long a time (average 114 hr) as P400 before local reaction necessitated changing the site. When P400 was infused in undernourished subjects without oral intake, balances of N, P, Mg, and Ca/70 kg of body weight per day were strongly negative (-4 g, -0.4 g, -6 mEq, and -0.2 g, respectively), whereas balances of K were about zero and those of Na and Cl were positive. Weight loss occurred. In the same patients, P900 containing 5 mg of cortisol/liter converted balances of N, P, Mg, and K to positive, and stimulated weight gain. Comparison of P900 (containing cortisol) and C1,800 in three emaciated subjects showed that the latter fluid caused a 2 to 4 times greater degree of positive balance in N, P, K, and Mg than the former. Comparison of P900 (containing cortisol) + 670-1700 cal by mouth with C1,800 in four undernourished subjects showed no statistically significant difference between these two programs. CONCLUSIONS by adding 5 mg of cortisol/liter to P900, the fluid can be infused through peripheral veins. P900 is intermediate in nutritional value between P400 and C1,800. P900 without oral supplement prevents negative balance of all elements except Ca. P900 + daily oral intake of 670-1700 cal is nutritionally equivalent to C1,800.