Sera from 58 pregnant women and 34 female university students were tested by a haemagglutination-inhibition (HI) method to determine the levels of immunity to rubella and to assess factors important in its epidemiology. Ages of women ranged from 15 to 35 years. Pregnant women were from the lower socio-economic groups, whilst students came from middle and upper income families. In both groups immunity to rubella increased with age. Students were more susceptible to the infection than pregnant women (21% compared with 3% respectively) - p less than 0.05 and the geometric mean titre was significantly higher in pregnant women than in students. Since women were of the same ages and essentially from the same geographical location, it is suggested that differences in susceptibility rates to rubella were due to differences in the socio-economic status of the two groups.