Acetic acid-zinc-formalin: a safe alternative to B-5 fixative.

B5 fixation achieves superior morphologic detail. However, environmental concerns have led to labor-intensive and costly requirements for disposal of mercury-containing fixatives. We performed a blinded prospective study to find a safe, mercury-free alternative to B5. Morphology was evaluated with 6 fixatives, including B5, in a blinded fashion. Acetic acid-zinc-formalin (AZF) was selected for further evaluation of immunohistochemistry, in situ hybridization, and molecular analysis. AZF fixation resulted in overall staining and morphologic detail comparable to B5 and achieved equivalent or superior antigen preservation for immunohistochemical studies. Strong signal intensity was achieved with in situ hybridization, and DNA amplification could be successfully performed. AZF allows greater flexibility in fixation times, decreases decalcification time, and eliminates labor-intensive steps required for B5 processing.