Electrodes modified with a layer of baker’s and wine yeast Saccharomyces cerevisiae (dried at various temperatures) were investigated as amperometric biosensors for lactic acid in the presence of mediators such as potassium ferricyanide, phenazine methosulphate, 1,2-naphthoquinone-4-sulfonic acid sodium salt and p-benzoquinone. Potassium ferricyanide was found to be the most suitable mediator in terms of electrode sensitivity and stability. The linear range of the current responses to the concentration of lactic acid was up to 1 mM. The relationship of electrode responses to lactic acid and viability of yeast cells was investigated.