The greatest increases in S. bacillaris biomass were obtained in aerated and non-aerated cultures where the introduced inoculum contained 60-130 or 60-160 mg DW L-1, respectively. The application of inocula exceeding 160 mg DW L-1 brought about a rapid inhibition of biomass increase and growth rate, and also extended the lag phase. The dilution of the medium restored the ability of exponential growth in the culture. It seems that in cultures inoculated with large inocula the reduced growth of S. bacillaris was induced by autoinhibition.