ABSTRACT: The microbial safety of cosmetic products is an important consideration. The results of preservation challenge test are required for the safety assessment. Different methods are commonly available and used in the cosmetic industry. These methods are different in the type of microorganisms used, the inoculation of samples, the criteria of acceptance, and the consideration of preservative stability. They will be compared by applying them on a Q 10 containing body lotion. Using borderline concentrations of the preservative system shows how different criteria of acceptance lead to different assessments. However, in order to fix the period after opening (PAO) additional data beside the microbiological challenge test have to be considered.