The diagnosis of prostatic carcinoma and especially minimal prostatic carcinoma can sometimes be challenging on needle core biopsy and occasionally immunohistochemistry is an aid in the diagnosis. Immunostains, such as those directed against the basal cell marker p63 and, more recently, employing antibodies reactive with alpha-methylacyl-CoA racemase (AMACR), can be useful in this situation. The aim of this investigation was to assess the diagnostic utility of a p63/AMACR antibody cocktail and compare the staining pattern it produces with that using the individual antibodies alone. A retrospective review of 31 consecutive radical prostatectomy specimens and 150 prostate needle biopsy samples was performed to select histologic sections showing foci of prostatic carcinoma and/or minimal prostatic carcinoma, high-grade prostatic intraepithelial neoplasia (HGPIN), as well as common benign mimickers of prostatic carcinoma, to include atrophy and basal cell hyperplasia, especially with prominent nucleoli. Serial histologic sections from the corresponding paraffin blocks were stained with hematoxylin and eosin and by immunostains for p63, AMACR, and a prediluted antibody cocktail comprising both. The diagnostic utility of the cocktail was assessed, and the staining characteristics it produced were compared with those using the individual immunostains. In 430 foci, the cocktail produced a p63 staining profile identical to that using the single p63 antibody. Distinction of the nuclear p63 signal from the cytoplasmic AMACR localization was readily accomplished. There was an excellent agreement (kappa=0.91; P<0.0001) between the AMACR staining profile using the cocktail and the single AMACR antibody alone. The cocktail was very useful in highlighting prostatic carcinoma associated with HGPIN, flat and cribriform HGPIN, and distorted foci of minimal prostatic carcinoma. These data indicate that use of a p63/AMACR cocktail is essentially equivalent to use of each antibody separately for immunohistochemical confirmation of a diagnosis of prostatic carcinoma in needle biopsy. This cocktail would be of diagnostic utility when only limited tissue is available for immunohistochemical evaluation of small, diagnostically difficult foci in prostate needle biopsy tissue.