Clinical studies of ether-split influenza antigen vaccines have been in progress for almost a decade. One series of such studies, completed before the Hong Kong virus appeared, compared identically constituted conventional and antigen vaccines for serological effectiveness in 1700 vaccinees from the staff of a metropolitan hospital. A series of 6 annual trials included both "old" subjects (vaccinated the previous year) and "new" subjects (no vaccination the previous year). The serological response to the type A2 component of the antigen vaccines was 3-4 times better than that to intact virus in both the old and new populations. The response to either vaccine by new subjects significantly exceeded the response by the old subjects. The type B component of both vaccines induced an equivalent response in both populations. Monovalent Hong Kong vaccines, both conventional and antigen, given just prior to the Hong Kong epidemic induced an anamnestic response in a geriatric group. No influenza-like disease was seen in this high-risk group during the epidemic.