In most patients with chronic Chagas disease the Trypanosoma cruzi has been shown to be present in extremely scanty numbers in all tissues extensively studied using conventional non-specific histologic techniques presently available. The present work was carried out in order to compare the immunocytochemical method of peroxidase anti-peroxidase (PAP) with the Haematoxilin and Eosin (HE) technique in the quantification of the parasitism in formalin fixed tissues from chronic chagasic patients. Using the same tissue fragment from each one of 3 cases of chronic chagasic cardiomyopathy, sections were obtained for HE (average: 100 sections per fragment) and for PAP (average: 70 sections per fragment). The fragment from case Nip. 1 was first studied in 1952 and presented with relatively great number of parasites. The results, expressed as amastigotes nests per 100 sections stained by HE and PAP were, respectively (HE — PAP): case No. 1, 80 — 171; case No. 2, 5-116 and case No. 3, 1-2. The present results show that the immunocytochemical method improves the quantitative evaluation of the parasitism in tissues of chronic Chagas disease. Furthemore. it should be preferred not only for the specific diagnosis taut also for quantitative studies on the tissular parasitism even in those tissues included in paraffin wax for long periods of time.