Over a 2-year study period 5,858 public antenatal patients were screened with the Welcome hepatitis B surface antigen HA screening kit; 52 (0.89%) were positive (carriers) and 45 (87%) of these were identifiable as high risk patients and would have been diagnosed by selective screening; the remaining 7 (13%) would have been missed. Using a subsample of 1,000 women, it was found that high risk factors were present in 237 (23.7%). Restriction of screening to the high risk group cost an estimated $97 per carrier identified; universal screening cost $354 to identify each carrier. Screening only the high risk group would have missed the 7 carriers in the low risk group, which was estimated to number 4,470 patients (76.3% of the total). Estimated cost of screening the low risk group was $14,036, or $2,005 per carrier identified. The advent of highly effective vaccines enables the almost complete prevention of vertical transmission of hepatitis B. In mid-1988, vaccine costs in terms of hepatitis B prevention per baby were estimated to be $2,432 for vaccination of babies born to mothers in the high risk group, irrespective of maternal serology; and $9,729 for universal vaccination. Carrier rates vary between populations. For our clinic patients, universal screening and vaccination of all babies of high risk group mothers are considered appropriate. Selective screening may be more appropriate in a low risk private practice.