The authors evaluated the effectiveness of computer-generated telephoned reminders used to raise the rates of on-time immunization among preschool-age children in two public clinics in Atlanta, GA. The overall effect of the intervention on immunization levels appeared to be minimal (crude relative risk = 1.07, 95 percent confidence interval = 0.78, 1.46), in part because only about 80 percent of children in both the randomly selected intervention group and in the control group were members of a household with a telephone number listed in clinic records. However, logistic regression analysis indicated that 36 of 68 children (52.9 percent) in the intervention group whose households were reached were vaccinated within 30 days of their due dates, compared to 31 of 75 children (41.3 percent) in the control group whose household telephone numbers were recorded but not called (adjusted odds ratio = 2.12, 95 percent confidence interval = 1.01, 4.46). This analysis indicates that telephoned reminders demonstrated a level of effectiveness in improving immunization levels at inner-city clinics that recommends further trial and study.