Glutamine controls HCG production in shake flask and continuous culture systems. The total content and specific productivity of HCG on days 1, 3 and 5 of shake flask culture with 0 mM, 4 mM and 8 mM glutamine supplementation (white, black and grey, respectively, A and B, * = p < 0.05, ** = p < 0.01). Total content and specific productivity of HCG during continuous cultivation with varying glutamine concentrations (C and D, respectively). Boxes are used to illustrate the steady state examined. Panels A and B, n = 6; panels C and D, n = 3.