Results of studies on the disruption of cells depending on the concentration of microorganism suspension are presented. Studies were conducted using baker's yeast Saccharomyces cerevisiae. The process was carried out in a horizontal bead mill. The cell disruption kinetics was determined based on the number of living microorganisms. Computer microscopic image analysis was applied. It was proved that growing disruption rate constants of cells which appear with an increase of the concentration of microorganisms suspension excludes a possibility of using a linear description of general process modelling. Based on the analysis of cell size distribution and spatial location of yeast cells in the continuous phase, it was found that the mutual relations between cells intensified with an increase of their concentration. The initial number of cells and their disintegration degree has an influence on the process run. Hence process conditions change during the disintegration. A non-linear model based on mass transfer described cell wall disruption. Hypotheses concerning a non-linear run of the process are given. (c) 2007 Elsevier Ltd. All rights reserved.