Introduction. We have recently introduced silver enhancement of colloidal gold probes for the labelling of biological surfaces in scanning electron microscopy (Scopsi et al., 1986). We describe here how the same enhancing technique can advantageously be applied on semithin and ultrathin cryosections. Materials and methods. Rat pituitary glands were immersion-fixed for 15 min in 8% paraformaldehyde, cryoprotected in sucrose and frozen in liquid N (Tokuyasu,l978). Semithin and ultrathin sections were cut with a Sorval3 FS 1000 cryo-ultramicrotome and transferred, on a sucrose drop, to, respectively, poly-L-lysine-coated glass slides and Formvarcoated, carbonized 200 mesh nickel grids. In all of the subsequent steps grids were floated on drops and transferred by means of a platinum loop. Care was taken in order to maintain their back-side dry. All specimens were rinsed in ice-cold phosphate buffered saline containing 1% newborn calf serum and immunostained with a polyclonal rabbit anti-laminin serum (Wewer et a1.,1981) and 5 nm gold-labelled goat antirabbit IgG (Janssen, Life Sci. Prod., Beerse, Belgium). Ultrathin sections were post-fixed for 10 min. in 2% glutaraldehyde. Ultrathin and semithin sections were rinsed 3 x 10 min. in redistilled water and subjected to physical