The effectiveness of non-surgical treatments is depending on the oxygenation status of the tumor. The oxygenation status is determined in part by whether the bloodsupply is arterial or venous in origin, if the blood is distributed homogenously troughout the tumornetwork, and if there is fluctuations in the bloodstream. We have looked at some of these parameters for the malignant melanoma xenographt, using the mouse dorsal window chamber and a fluorecent cell line. We have also developed a techinque where we follow a bolus of contrast as it moves through the tumor vessel network. This first pass imaging technique has not been combined with vital microscopy before.We found that the first bloodsupply to the tumor was arterial in origin, and it remained so troughout the entire test periode. The blood reached some parts of the tumour with a time lag compared to other parts of the tumor. We also found that the blood passes through the tumor tissue significantly faster than through the normal muscle tissue.In short, the tumor is supplied by blood with high oxyhaemoglobin saturation that moves quickly through it; this speaks in favor of the tumor being well oxygenated. In contrast, some areas of the tumor recives blood that has passed through a longer stretch of vessel than other parts, and these parts will consecuently be more at risk for hypoxia than other parts if the oxyhemoglobin saturation or blood flow is reduced. Hypoxic regions in a tumor select for more malignant and metastaic cells, and diminishes the effect of non-surgical treatment.