Purpose Early metabolic response with a decrease in glucose demand after cytotoxic treatment has been reported to precede tumor volume shrinkage. However, preclinical studies report of a very early rise in metabolism, a flare, following treatment. To elucidate these observations, we performed an experimental study on early metabolic response with sequential analysis of metabolic changes. Methods Three squamous cell carcinoma cell lines and one nontumorigenic cell line were exposed to cisplatin. The uptake of the fluorescent glucose analogue 2-NBDG was examined at days 1.6 using fluorescence microscopy. The relation between 2-NBDG-uptake and cell survival was evaluated. Results The tumor cells exhibited a high uptake of 2-NBDG, whereas the uptake in the nonmalignant cells was low. The more cisplatin sensitive cell lines exhibited a more pronounced metabolic flare than the less sensitive cell line. Conclusion A metabolic flare was a very early sign of treatment response and potentially it could be used as an early marker of treatment sensitivity.