The addition of 2% phenol had a marked accelerating effect on neutral buffered 4% formaldehyde as a fixative. Histopathological material fixed in buffered phenol-formaldehyde (pH 7.0) and rapidly advanced to paraffin in an enclosed tissue-processor showed improved nuclear and cytoplasmic detail, reduced shrinkage and distortion, and an absence of formalin pigment. Good results were obtained in less time when sequential fixation in phenol-formaldehyde buffered to pH 7.0 and pH 5.5 was carried out at an elevated temperature (40 degrees C) in the enclosed tissue-processor. Standard histological stains and immunoperoxidase methods worked well. In resin-embedded tissue, buffered phenol-formaldehyde (pH 7.0) gave satisfactory ultrastructural results. The penetration rate of buffered phenol-formaldehyde (pH 7.0) in gelatin models did not differ from that of neutral buffered 4% formaldehyde. Polyacrylamide gel electrophoresis showed enhanced protein polymer formation with buffered phenol-formaldehyde (pH 7.0) as compared with neutral buffered 4% formaldehyde. Protein polymer formation increased in response to increased time and temperature. Cells fixed in suspension in buffered phenol-formaldehyde (pH 7.0) and neutral buffered 4% formaldehyde showed similar volume changes.