The influence of pH on the germination characteristics and the microscopic morphology of Trichoderma reesei QM 9414 has been investigated. The parameters of a kinetic model were estimated by fitting model simulations to morphological measurements during submerged cultures at different pH values. Both the tip extension rate and the branching frequency varied with the pH and had maximum values around pH 4.5. The time of spore germination was dependent on the pH, but within the used pH-range (2.2-7.6), no significant effect of pH on the fraction of viable spores was observed.