A study of the safety and immunogenicity of two different recombinant DNA yeast-derived hepatitis B vaccines was conducted in 90 young adults according to a 0-, 1-, and 6-month vaccination schedule. Preliminary results using the 20 micrograms SmithKline Biologicals or 10 micrograms Merck Sharp & Dohme recombinant yeast-derived hepatitis B vaccines indicate that both vaccines are clinically safe and immunogenic. Only minor side effects have thus far been reported. Seroconversion rates among vaccine recipients were 80% or greater after the first two injections with either vaccine, and 100% after the third dose of the SmithKline Biologicals recombinant DNA hepatitis B vaccine.