SIMAGE: simulation of DNA-microarray gene expression data. Software overview: The SIMAGE web site [5] consists of three parts: (i) a start page where the user may upload parameters for a simulation; (ii) a web-page where the user specifies a number of parameters, after which (iii) the results, namely simulated data (see below), are presented. Each run is assigned a unique session, which allows the user to inspect the results at any given time. SIMAGE provides the user with three types of text files containing: (i) the parameters used for the simulation. This file can, in turn, be provided to SIMAGE for future simulations; (ii) the (differential) gene expressions, which are obtained after applying only the gene-layer; and (iii) the observed signals (including their location on the slide and the corresponding genes) after applying the layers explained in the following paragraphs. The estimates from a provided dataset are determined by a self-explanatory web site which is linked from the SIMAGE web site. SIMAGE was written in Pascal and compiled by FreePascal version 1.0.10 [6]. Estimates for parameters, based on real data, are provided by a script developed in R [7]. The software requires an Apache web-server and is integrated with a PHP web-interface.