Temporal heterogeneity in blood perfusion is a common phenomenon in tumors, but data characterizing the nature of the blood flow fluctuations are sparse. This study investigated the occurrence of blood flow fluctuations in A-07 melanoma xenografts by using gadopentetate dimeglumine (Gd-DTPA)-based dynamic contrast-enhanced MRI (DCE-MRI). Each tumor was subjected to two DCE-MRI acquisitions separated by 1 hour. The data were processed by Kety analysis and resulted in two E · F images (E is the initial extraction fraction of Gd-DTPA and F is the perfusion) and two λ images (λ is the partition coefficient of Gd-DTPA) for each tumor. The E · F images were used to determine the changes in blood perfusion arising in the time between the two imaging sequences. The λ images were used to control the reproducibility of the experimental procedure. The study showed that DCE-MRI with subsequent Kety analysis is a useful method for detection of blood flow fluctuations in A-07 tumors, and strongly suggested that the peripheral regions of A-07 tumors are more exposed to temporal changes in blood perfusion than are the central regions. Magn Reson Med 58:473–481, 2007. © 2007 Wiley-Liss, Inc.