No influenza-A virus epidemic occurred in the Federal Republic of Germany during 1971-1975. The neighbouring countries, however, reported up to three such epidemics. The vaccines used had differences: contrary to neighbouring countries, in the FRG largely those were used which had mineral adjuvants, and they more frequently had viral subgroups. Comparison between the USA and FRG with respect to influenza death-rates over 20 years revealed a strict correlation from 1956 up to 1965. But since 1966 the death-rate has decreased progressively in the FRG while it has remained unchanged in the USA. Immunisation methods in the two countries have differed since 1966 in that the Public Health Authorities of the two countries have recommended immunisation of different population groups: in the USA it has been only for patients at risk, while in the FRG the rest of the population has also been urged to be immunised. As a result, immunisation rates differ markedly between the two countries. Absence of an influenza epidemic, accompanied by a reduction in death-rate due to influenza, strongly suggests that the two phenomena are the result of a break in the infection chain. This seems to be more successful when both part of the total population and the risk groups are immunised.