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The need to combine qualitative description and quantitative data is stressed and the interest in comparing them is emphasized in histophysiological studies of teleost endocrines. The pituitary gland has a rather complex structure; the numeration of the various cell types is slow, tedious, and not very informative. Cytological and histochemical processes are more often used to examine histological modifications after experimental treatments or during fish migration. Since thyroid gland, interrenal and islets of Langerhans are not individualized in teleosts, their histophysiological study is more difficult than in mammals, and their weight changes are impossible to evaluate. Caryometric determinations were performed, as well as measurements of epithelial cell height of the thyroid gland, and autohistoradiographic studies were made. The determination of the number of follicles shows that salmon thyroid is larger than trout thyroid, and this difference in size may partly explain why salmon is more difficult to radiothyroidectomize than trout. Planimetric and caryometric studies and numeration of cell nuclei belonging to a constant area of interrenal tissue were undertaken. The quantitative data were submitted to statistical evaluation and their significance was established. These criteria demonstrate that interrenal is strongly stimulated after a treatment with metopiron, aldacton or reserpin; conversely, hypophysectomy or cortisol administration reduces this activity. A transfer into distilled water induces only a slight stimulation. The transformation of a sedentary parr into a migrating smolt (Salmo salar) is accompanied by a hypertrophy of adrenals, temporarily reinforced after a transfer into seawater. Corpuscles of Stannius and endocrine pancreas were also submitted to planimetric or caryometric studies and results are briefly discussed. [ABSTRACT FROM AUTHOR]