Medetomidine sedation is a common anesthetic regimen for rodent fMRI studies. However, depth and duration of the sedation may prove insufficient for MR imaging. Adding isoflurane is an efficient way to increase depth and duration of sedation. In rats we varied the concentration of additional isoflurane (0 - 1.5 %) and performed 1D line scanning upon electric forepaw stimulation to characterize the effect of increasing isoflurane on amplitude and onset of the BOLD response. While low concentrations did not significantly alter amplitudes or onsets, we found severely reduced amplitudes and delayed onsets for higher concentrations (> 0.7 %) of isoflurane.