Between February 1984 and August 1986 results have been obtained in 58 completed or ongoing clinical studies by 33 investigators in 19 countries on a yeast-derived recombinant DNA hepatitis B vaccine (Engerix-B). Among the 6100 subjects enrolled in these studies, 5664 subjects (150 normal neonates, 178 neonates of hepatitis B carrier mothers, 330 children aged 3-10 years, 3697 young healthy adults, 438 homosexual males, 110 older healthy adults, 139 drug addicts, 262 institutionalized mentally retarded patients, 59 thalassaemics, 25 sicklaemics, 270 patients on chronic haemodialysis and 6 haemophiliacs) received one or more (up to 4) injections of different doses of the yeast-derived vaccine according to either a 0, 1, 2, and 12 month or a 0, 1, and 6 month vaccination schedule. In randomized comparative studies 436 subjects received either one of two commercially available plasma-derived vaccines. The results reviewed in the present summary have shown that Engerix-B is safe, clinically well tolerated, gives an anti-HBs response which is qualitatively and quantitatively similar to that obtained with plasma-derived vaccines and confers protection against infection and disease. Engerix-B can be considered as a valid alternative to existing hepatitis B vaccines.