In order to perform morphometric analysis of the nasal (salt) glands of domestic duck it was necessary to standardise the regime of fixation and processing for this tissue. This paper reports the results of these experiments in which the nasal glands of nine groups of ducks were perfused by fixatives containing various concentrations of glutaraldehyde; each group included three secreting ducks and three non-secreting control ducks. Fixative osmolality ranged from 300-825 m-osmol. The resulting effects on the electron microscopical appearances of mitochondria and intercellular spaces were assessed. The fixative finally selected as most satisfactory for both control and secreting tissue contained 3.5% glutaraldehyde and 3% dextran in sodium cacodylate buffer, giving an osmolality range of 580-650 m-osmol.