Lateral diffusion of lipids and proteins in yeast plasma membranes has been reported to be anomalously slow, and implicated as a possible reason for polarization in yeast. In order to gain insight into the observed slow diffusion in yeast membranes, we explored lateral diffusion of two proteins of different origin. We compared lateral dynamics of the Candida drug resistance protein-1 (Cdr1p), and the human serotonin(1A) receptor (5-HT1AR) by fluorescence recovery after photobleaching (FRAP). Our results show that while Cdr1p-GFP displays slow diffusion, the diffusion of 5-HT1(AR)-EYFP is significantly faster. Interestingly, upon ergosterol depletion, the mobility of Cdr1p-GFP did not exhibit appreciable change, while 5-HT1(AR)-EYFP mobility showed an increase. On the other hand, upon actin cytoskeleton destabilization, the mobile fraction of 5-HT1(AR)-EYFP showed considerable increase, while the mobility of Cdr1p-GFP was not altered. Our results represent the first report on the dynamics of the important drug resistance protein Cdr1p and provide novel insight on diffusion of membrane proteins in yeast membranes. (C) 2009 Elsevier Inc. All rights reserved.