Actin filaments (F‐actin) are protein polymers that undergo rapid assembly and disassembly and control an enormous variety of cellular processes ranging from force production to regulation of signal transduction. Consequently, imaging of F‐actin has become an increasingly important goal for biologists seeking to understand how cells and tissues function. However, most of the available means for imaging F‐actin in living cells suffer from one or more biological or experimental shortcomings. Here we describe fluorescent F‐actin probes based on the calponin homology domain of utrophin (Utr‐CH), which binds F‐actin without stabilizing it in vitro. We show that these probes faithfully report the distribution of F‐actin in living and fixed cells, distinguish between stable and dynamic F‐actin, and have no obvious effects on processes that depend critically on the balance of actin assembly and disassembly. Cell Motil. Cytoskeleton 2007. © 2007 Wiley‐Liss, Inc.