A mixed-longitudinal study was carried out in the 1985 Dutch birth cohort of macrobiotic infants aged 4-18 months (n = 53) and 57 omnivorous control infants matched for month of birth, sex, parity, educational level of the father and the residential area. Study methods included regular anthropometric measurements and a psychomotor testing. Reported birth weight was 180 g lower in the macrobiotic group than in the control group and was positively associated with maternal weight increase during pregnancy. Between 4 and 18 months of age, mean values for all anthropometric parameters were considerably lower in the macrobiotic infants. From birth to 4 months, weight gain was less in macrobiotic infants, and from 6 months the rate of growth in weight and length decreased further, reaching its lowest value between 8 and 14 months of age. A similar pattern was also observed for other anthropometric parameters. Between 8 and 14 months, arm circumference showed an absolute decrease. During this period, increase in arm muscle mass in the macrobiotic group was only half of that in the control group. From 14 months of age, growth stabilized parallel to the 10th percentile of the Dutch references. Gross motor and language development were also slower in the macrobiotic infants. The paediatrician observed major wasting of skin and muscles in 30 per cent of them. The growth rate for weight and arm circumference was independently associated with the energy intake and the protein content of the macrobiotic diet. Growth in length was positively associated with protein content of the diet, but not with energy intake.