This work aims to test the efficiency of hand instrumentation allied to paramonochlorophenol dressing in cases of pulp necrosis, when this substance is diluted in water and alcohol, propylenoglicol and glycerin. Superficial pression and pH were verified to test them afterwards facing to bacteria that could be found in infected root canals and avaible to study in our bacteria lab. Solution more effective "in vitro" and of less cytotoxicity "in vivo" were selected to be employed in patients from the Dental Clinics at School of Dentistry--Federal University of Minas Gerais. It was concluded that: 1. the relationship between cytotoxicity and bacterial activity was proportionally the reverse to superficial pression, except to Hydropropylenic solution of PMCF 5% and 10%; 2. in the study with patients (40 cases) the growth anaerobic microorganisms were present in 97.5% of examined teeth; 3. from solutions used for intracanal dressing hydroalcoholic solution of PMCF at 5% was the on which showed more effectiveness; 4. studies must be carried out on glycerin solution of PMCF, to turn viable its employment in Endodontia.