The merits of formaldehyde, formaldehyde-glutaraldehyde combinations, and glutaraldehyde in phosphate buffers have been compared as fixatives that will give easy and satisfactory preservation of tissues for routine automated histologic processing and yet keep them suitable for electron microscopical studies after prolonged storage at room temperature. We recommend a combination of 4% commercial formaldehyde and 1% glutaraldehyde in a buffer of 176 mOsm/liter. Tissue sections should not exceed 3 mm in width, and tissues to be examined by electron microscopy should be taken from the outside of the tissue sections. All special stains performed at light microscopical level gave satisfactory results. The fixative should be stored at 4 C and is stable for at least three months. The superior cross-linking features of glutaraldehyde are retained, while the concentration of glutaraldehyde is low enough not to substantially obscure the PAS reaction.