We study collaborative modeling of business processes with respect to the impact of tool support on the modeling process. For this purpose we compared model quality and modeling costs in two cases. The first was carried out with the help of a collaborative modeling tool; in the second case we kept all other parameters as closely as possible to the first one but conducted the modeling session in the usual way without tool support. We observed a marked increase in modeling time in the second case and a reduction in model quality. Categories and Subject Descriptors I.6.5 [Model Development]: Modeling methodologies General Terms Management, Documentation, Design. Keywords Computer-mediated communication and collaboration, systems design and implementation, business process modeling.