The major genera found in the microflora of fermented, sour, cassava-starch were Streptococcus, Bacillus, Lactobacillus and Saccharomyces with amylase activity. Lactic acid bacteria predominated whereas the presence of moulds was not significant. No coliforms were detected. Electron microscopy showed bacteria and yeasts in contact with the starch granules and signs of erosion on the granule surface. Lactic acid was the main metabolite; no oligosaccharides, maltose or glucose were detected, indicating their rapid utilization. The degree of acidification, which correlated with the decrease in viscosity and the final quality of the product, was influenced by the variable microbial ecology.