In this paper the experiments on microbiological quality and aroma components of yoghurt samples produced from long life goat's and cow's milk, and also from milks with 2% milk powder addition, during 9 days of refrigerated storage are described. Milk fermentation was conducted at 42 °C for 6 h. During days 1, 3, and 9 of storage the changes in acidity (pH value and lactic acid percent), viable counts of streptococci and lactobacilli and aroma components (acetaldehyde and diacetyl) were determined. Lower pH values and smaller lactic acid concentrations were found in control yoghurt samples. Viable counts of streptococci decreased during storage (from 1.01×10 8 to 3.97×10 7 CFU ml -1), whereas the viable counts of lactobacilli increased in all samples (from 6.95´10 6 to 2.32×10 7 CFU ml -1). The increase in count of lactobacilli was the greatest in goat's milk yoghurt samples. On the ninth day of storage, ?logN between cow's and goat's milk yoghurt samples was 0.2. Acetaldehyde in yoghurts decreased during storage time from 5.47 mg kg -1 (on day 1) to 1.05 mg kg -1 (on day 9). Both control yoghurt samples had lower acetaldehyde concentration than the supplemented samples. During nine days of storage, a significant increase in diacetyl content of yoghurt samples (from 14.20 mg kg -1 on the first day to 18.65 mg kg -1 on day 9) was noticed. goat's milk yoghurts, especially that manufactured without milk powder addition, had very soft consistency, but no syneresis was observed.