Present methods of counting and sizing of bacteria arc usually tedious and often have low statistical validity. The objective of this thesis was to investigate the feasibility of counting and sizing of bacteria with the Coulter Counter and to evaluate orifices which were prepared in this laboratory. Size distributions of Pasteurella multocida and Proteus vulgaris were obtained with the electronic particle counter. These distributions appeared to follow the normal distribution when relative per cent was plotted against diameter, The two modes of the distributions appeared far enough apart to warrant future attempts to separate quantitatively <i>P. vulgaris and P. multocida </i>in mixed suspensions. Size distributions also were obtained for <i>Staphylococcus epidermidis, Sarcina lutea,</i> and <i>Azotobacter</i>. Many variables appeared to be inherent in the electronic particle method of counting biological cells; among these are the biological cells, diluent, and electronic circuitry. Apparently the variability in the electronic circuitry caused the calibration of laboratory orifices to be impossible according to conventional methods. / Master of Science