Abdominal lavage is used in laboratory rodents for a variety of applications but carries an inherent risk of abdominal organ laceration; therefore, personnel carrying out this procedure must have considerable expertise. In this paper, the authors describe an improved method for delivering sterile media to and collecting peritoneal fluids from dark-clawed Mongolian gerbils (Meriones unguiculatus) that had been peritoneally infected with filarial nematode parasites (genus Brugia). To carry out this gravity-assisted technique, the authors used a catheter to introduce sterile media into the peritoneal cavity of each gerbil and then to passively drain peritoneal fluid and larval worms for collection. Average fluid recovery was consistently greater when using this gravity-assisted method than when using aspiration. Larval parasites were recovered by both methods. To recover large volumes of fluid using the standard method of abdominal lavage, personnel typically must euthanize rodents. This gravity-assisted technique allows researchers to collect large numbers of parasite larvae without euthanizing gerbils.