Fluorescence in situ hybridization (FISH) is used to determine amplification status of the Her-2/neu gene in specimens of newly diagnosed breast carcinoma. The Vysis kit for FISH analysis stipulates that the tissue be formalin-fixed and paraffin-embedded. Concerns regarding carcinogenicity of formalin and environmental effects of formalin waste have led to the development of formalin replacement products. An increasing number of breast biopsy specimens are being fixed in these substitutes. We tested 6 non-formalin–based fixatives to determine their impact on FISH testing for Her-2/neu gene amplification status by comparison with formalin-fixed control specimens from the same neoplasm. Specimens fixed in Pen-Fix, Prefer, Histochoice, UniFix, and GTF were associated with absent or technically compromised staining in at least one of the 3 neoplasms tested for each fixative when compared to the formalin-fixed control. O-Fix did not seem to compromise staining quality in 3 paired specimens tested.