Bacteria alone or in combination with yeasts were found to be responsible for the fermentation of dosa — an indigenous Indian fermented food. Leuconostoc mesenteroides, Streptococcus faecalis, Lactobacillus fermentum and Bacillus amyloliquefaciens were the predominant bacteria responsible for souring and leavening of dosa batter. Yeasts whenever present, belonged mainly to Saccharomyces cerevisiae, Debaryomyces hansenii and Trichosporon beigelli. They produced flavour, enzymes and helped in the saccharification of starch. Both bacteria and yeasts were contributed by the ingredients Oryza sativa and Phaseolus mungo. The prevalence of bacteria and yeasts was affected by seasonal variations but bacteria always dominated the overall microbial load.