In New South Wales, health screening of school entrants provides the only mechanism for routine monitoring of immunisation uptake in children. School health nurses are in the best position to improve the compliance with immunisation at this age. We compared two interventions to be used by the nurses to increase immunisation uptake in school entrants who reported missing either the measles-mumps vaccine and/or the pre-school diphtheria-tetanus toxoid and oral polio vaccine boosters. Parents in the passive intervention group were sent a letter and leaflet encouraging immunisation; the active intervention group received a telephone reminder from the nurse in addition to the written materials. Both groups were followed up at a later date to assess final immunisation outcome. Of 817 children screened, 88.2% had been immunised against measles and 73.6% had received the booster; 239 children were randomised to the two interventions. Excluding children lost to follow up and those fully immunised at the start of the study, 20 (37%) of 54 were immunised following the passive intervention, and 35 (71%) out of 49 following the active intervention (P = 0.001). Receipt of the letter and leaflet was associated with an increased uptake of booster vaccination (P = 0.036). The active intervention required 14.7 telephone calls and 1.6 uses of the interpreter service per completed immunisation. The passive intervention resulted in worthwhile increases in immunisation rate with minimum cost. A greater improvement in immunisation outcome was achieved by the active intervention, but its use was labour intensive and may only be warranted if high immunisation rates in this age-group are given priority.