Abstract Summary: Microarray technology is now routinely used to monitor genome-wide expression profiles. However, current microarray imaging and analysis packages typically require manual intervention and assumptions on alignments. Unfortunately, limitations and assumptions are typically undisclosed and methods are not published. To facilitate exploration of image data, we developed SignalViewer. This paper presents a description of the application. Availability: SignalViewer is available at http://qge.fhcrc.org/signalviewer/ Supplementary information: Screenshots are available at the above location, along with downloads for Windows 2000 and Linux (Redhat 7.2).