Auckland Medical Research Foundation. 128 LETTERS TO THE EDITOR THE USE OF FORMALIN FIXATION IN AN IMPROVED METHOD FOR IMMUNOFLUORESCENCE HISTOCHEMICAL INVESTIGATION OF

Im munofluorescence histochemistry is now widely used for the detection of trace amounts of tissue antigens. In general, tissues are snap-frozen prior to sectioning on a cryostat. Recently, this technique has been applied to the demonstration of neurophysin in the hypothalamoneurohypophysial system of the pig (2), rat (6) and guinea pig (1). In a recent publication we showed neurophysin to be localized in the pen-karyon of cells of the magnocellular paraventnicular and supraoptic nuclei of the guinea pig (1). In addition, other cells groups including the supraoptic complex, accessory supraoptic nucleus and the acces-sony paraventnicular nucleus were found to contain neurophysin-like antigen. The freezing of tissues by plunging into eithe