Ferric chloride, when boiled with hydrazine hydrate and cacodylic acid, is converted into a fine cationic iron colloid. This colloid allowed good adhesion of biological micro-samples, inculuding the fixed ones, to the glass slips and facilitated the scanning electron micropscopy of these samples. The colloid was much more powerful in this mounting than the usually used and expensive poly-L-lysine. Living cells, such as human red blood cells, are esaily and sufficiently mounted with L-lysine or L-arginine on the glass slips.