AbstractBromcresol purple (BCP) dye has been used as a colored marker and pH indicator for 10% formaldehyde solution. Its distinctive coloring has advantages related to lab or hospital safety and tissue processing. The effects of the dye on tissue processing and staining were tested by routineuse for over 2 yr in a busy pathology laboratory, by fixative penetration (K-value) determinations on a protein model, and by pH indicator trials. No adverse effects were noted in these trials. Although BCP was reported to bind specifically with albumin, results of trials suggest that this property did not confer any advantage to rate of fixation nor did it affect routine staining. BCP is recommended as an additive to 10% neutral buffered formalin as a pH indicator for acidic conditions during fixation or storage that might produce artifacts. In addition, it serves as a marker for this toxic chemical. (The J Histotechnol14:257, 1991)