A Plexiglas isolator for rearing germfree vertebrates is described. Plastic components were precut and finished by a Plexiglas supplier. This equipment is relatively inexpensive; moreover, neither special facilities nor skills are required in their construction. Advantages of this type of isolator are: readily dismantled for cleaning, durable, excellent visibility of the interior, and minimal maintenance. In 30 separate groups of animals, 27 of these yielded germfree chicks. Many of these chicks were reared germfree for 4 weeks; and several were maintained for about 2 months, without microbial contamination. Pure cultures of Candida albicans, Streptococcus faecalis, and Clostridium perfringens were established as monocontaminations in the intestinal tracts of chickens. In contrast, Alcaligenes faecalis ATCC 9220 failed to grow in the gut of chicks, following peroral administration of this organism. All chicks described were employed on other experiments, and were killed for various assays at times specified.