The effects of T4 phage on the metabolic rate of resting cells of Escherichia coli B in a restricted medium during the early phase of phage infection were measured calorimetrically. Heat output rate (P) and total quantity of heat (Q) of culture, heat output rate (P-o) and quantity of heat (Q(o)) of single cell were determined. P and Q of E. coli-T4 phage system, or P-o and Q(o) of infected cell, are all higher than that of control. The metabolic activity of infected cell is enhanced by 45-62%. P has a linear correlation with cell concentration (C), P(mu W) = 1.68 x 10(-6)C(cfu/mL) + 1.86, for E. coli B cells, and for E. coliB-T4 phage system, P (mu W) = 2.24 x 10(-6)C(cfu/mL) + 3.60. Q does not change significantly with the change of cell concentration. But Q(o) decreases with C increasing, indicating that Q(o) is restrained by cell density. (C) 2005 Elsevier B.V. All rights reserved.