Methods were developed for aseptic maintenance of Cyprinodon variegatus fry for extended periods. Preliminary studies indicated that under optimum conditions sterile embryos develop normally for a sufficient time to function as carcinogenteratogen assay systems. An embryo-primary cell culture technique was developed that incorporates, in a single system, certain characteristics of both intact embryos and primary cell cultures and allows simultaneous observation of the effects of carcinogens on the whole organism and primary cell monolayers. The effective use of these systems provides one the opportunity to study the effects of carcinogens on teleosts at the cellular and organismic level.