In Chile swine trichinosis has presented a progressive decreasing in the last two decades of XX century. T. Spiralis pig infection descended from an average of 0.683 per 1000 in 1980-1984 to 0.315 in 1985-1989 andto 0.115 in 1990-1996. In the particular case of Metropolitan Region this decreasing has been more marked: from an average of 0.058 per 1000 in 1990-1994to 0.003 in 1995-1999. Between the end of June 1999 and middle January 2000 in MetropolitanRegion abattoirs T. spiralis was detected in 15 (4.9%) out of 306 swine from two pigsties located in El Monte (E.M.) and Padre Hurtado (P.H.) 45 and 30 km south-west from Santiago. In the same period another four pigs from the same premises were found infected in abattoirs of other regions. During inspection visits it was stated that both pig farms had deficient sanitary conditions. Phototrichinoscopy was positive in three out of five Rattus norvegicus collected in E.M. In pigsty PH the examination of diaphragm samples of 25 dogs and 17 cats resulted negative. In the premises originating T. spirali infected swine the Metropolitan Environmetal Health Service Abattoirs Progam carries out an epidemiological vigilance consisting in the follow-up of animls destined for slaughteringin order to initiate prophylactic actions oriented to eliminate eventual sources of trichinosis infection for human and rearing pigs