Virtually unlimited numbers of hydra can be grown under precise conditions in the laboratory with relative ease. Artemia cysts must be treated to remove gross contamination before hatching the nauplii to be used as the food of hydra. Large volumes of a variety of chemically defined culture solutions should be prepared. A particular regimen of animal care especially devised for aquatic invertebrates must be adhered to. General requirements for, and the advantages of, laboratory cultivation of aquatic invertebrates are discussed.