Several growth monitoring parameters, including adenine nucleotide contents, were measured during Escherichia coli K12 batch cultivation in mineral medium with glucose. The adenylate energy charge with its mean value of 0.83 remained roughly stable during growth. The total adenylate and ATP pools (nmol/mg dry weight), and also the individual cell volume changed with a pattern of two maxima at approximately 4 and 10 h of cultivation. After the exhaustion of the glucose from the growth medium the adenylate energy charge, the pools of ATP and total adenylate started to decrease marking the onset of the stationary growth phase. Our data indicate that actually there was only a limited period within the logarithmic growth phase during which the growth might have been balanced: during this period of 1.5 h different growth monitoring parameters (optical absorbance, cell number, total cell volume, and ATP content per ml) increased with almost equal rates. Moreover, as ATP pool and median cell volume during this short period were approximately constant, the culture might have been even in the steady state.