Proteins dissolved in a drop induce and enhance the pinning of the drop contact line. This effect dramatically increases the volume of drops that are vertically pinned on a flat siliconized substrate. It was found that this drop pinning behavior exhibits two regimes: for low protein content in a drop the pinning increases as the contact angle hysteresis increases, and for high protein content the pinning decreases as the surface tension of the protein solution decreases. (c) 2008 Elsevier Inc. All rights reserved.