The most objective analysis of measles herd immunity could be made by sero-epidemiological study. In the population of North-West area of Romania we have evaluated the measles immune protection through a seroprevalence study, using an age stratified sample of population in witch the subjects from Cluj and Bistriţa-Năsăud counties were voluntarily involved. The measles antibody concentration was determined by immunoassay method using Hycor test. The database was performed in Microsoft Access and the statistics in Epi Info 2000. Levels higher then 40 arbitrary units (the cut-off of protection) of the measles antibody were met in 80% (IC95% : 75.09-84.01) of all subjects, 82.4% of the females and 84.9% of the urban area peoples. 98.3% of all subjects had detectable antibody levels. The protection increased by age: the adults had protective levels in at least 90% of cases. Global vaccine efficacy was 64.7% (IC95 % : 56.5 - 72.9), moderately decreasing with increasing age (the correlation coefficient--58.1%). In the assessed sample, the measles protection was the highest in adults, women and subjects from urban areas. The vaccine efficacy was relatively small, but the majority of subjects had detectable titers of measles antibody.