Degree of binding reactivity to actin in variously fixed tissues was histochemically examined by using phalloidin and antiactin staining on paraffin or frozen sections of 5-day chick embryonic heart. Fluorescein-labeled phalloidin staining on frozen section of the specimens fixed with 4% formaldehyde showed intense staining of actin in the myocardium and the aorticopulmonary (AP) septum. However, phalloidin did not react to actin on paraffin sections of the specimens fixed with 4% formaldehyde, nor fixed with 4% formaldehyde and 1% tannic acid (TA). FITC-labeled antiactin staining on paraffin sections of the specimens fixed with 4% formaldehyde and 1% TA showed comparable fluorescent intensity with that of phalloidin staining on frozen sections. However antiactin staining on paraffin sections of the specimens fixed with 4% formaldehyde only showed reduction of fluorescent intensity around the Ap septum. Both phalloidin and antiactin react non-specifically to the tissues fixed with solutions including 1% glutaraldehyde. Since paraffin sections showed much better tissue preservation than frozen sections, we suggest that paraffin embedding with TA fixation is very useful for actin histochemistry using antiactin.