The numbers of yeasts in the effluent disposal system of the Prince Albert, Saskatchewan Pulp Mill occasionally reached 1 × 106 cells/liter, but were usually below 5 × 105 cells/liter. Rhodotorula species were commonly isolated and sometimes amounted to half of the population, though usually the relative numbers were considerably lower. The highest counts were found in late summer and early autumn. Bacterial counts varied from 20 × 106 to 74 × 106 cells/ml. Chemical O2 demand (COD) reached about 1200 mg/liter at times, and decreased as the effluent moved through the disposal system, about 40% of the total COD being removed during the treatment process. A considerably wider range of yeast species was found in the pulp mill disposal basins than in the Saskatoon sewage treatment plant. Most of the ascosporogenous yeasts found were Hansenula or Pichia species usually occurring in association with trees, as were many of the Candida species isolated.