It is said that HER2/neu expression by immunohistochemical analysis varies with the time of fixation. The purpose of this pilot study was to determine the impact of the length of fixation in 10% buffered formalin on the expression of HER2/neu by immunohistochemical analysis. We studied tissue samples from 10 invasive breast cancer cases after fixation for 3, 48, 72, 96, and 120 hours. The tissue was processed immediately after fixation, resembling routine practice. The 50 resulting blocks were then batch stained with PATHWAY HER2/neu clone 4B5 rabbit monoclonal antibody using the Ventana Ultraview DAB detection kit in a Ventana BenchMark XT processor (Ventana, Tucson, AZ). The stained slides were reviewed and scored. We found no significant difference in the intensity of the stain or the percentage of cells stained regardless of the time in fixation. Fixation times between 3 and 120 hours in 10% buffered formalin do not appear to have an impact on the expression of HER2/neu by immunohistochemical analysis.