Infant feeding practices and related factors were studied in a survey of 189 mothers of 4-month-old infants in 1980 and of 151 mothers of 6-month-old infants in 1982. In both groups about 70% of the mothers commenced with breast-feeding. In 1980, 21% of the infants were still being breast-fed at the age of 4 months, compared with 32% in 1982. 26% of the infants were still being breast-fed at the age of 6 months. The most frequently mentioned reason for not commencing with or discontinuing breast-feeding was 'insufficient milk'. Univariate analyses showed that the educational level of the mother and her smoking habits were significantly related to both the commencement and the duration of breast-feeding in 1980 and 1982. These results were confirmed by multivariate analyses which suggest that well educated, non-smoking mothers are the most successful in breast-feeding their infants.