Biomass quantification methods provide little information about the health of a cell culture. XTT is capable of quantifying culture activity by forming an orange colored formazan in the presence of active mitochondria. While XTT has been used to measure MIC's of fungicides, there has been no study proving XTT's ability to detect the impact of bioprocess related stresses on metabolic activity. This study shows that XTT can quantify the decrease in metabolic activity due to elevated temperature, shear stress, and microwave treatment.