The influence of various feeding patterns on physical growth and mental development of the infant, particularly during the first 6 months of Life, is an important subject. Head circumference values of 172 healthy new-born infants were included in the study; 62 were exclusively breast-fed (BF), 58 were mixed-fed (MF) and 52 were formula-fed (FF). No significant differences were found in head circumference values between the groups at birth (BF 35.2+/-0.1, MF 35.1+/-0.1, FF 35.0+/-0.1 cm for boys and BF 35.0+/-0.1, MF 34.9+/-0.1, FF 34.8+/-0.1 cm for girls). At the end of the first month, the infants in the BF group (38.3+/-0.1 cm and 37.9+/-0.1 cm for boys and girls, respectively) had strikingly greater head circumference measurements than the others (MF 36.7+/-0.1, FF 36.6+/-0.1 cm for boys and MF 36.5+/-0.1, FF 36.4+/-0.1 cm for girls) (P < 0.05). However, in the subsequent 4-month period, the values detected in each group were almost the same. At the sixth month, head circumference-for-age values of infants in MF (42.6+/-0.1 cm for boys, 41.4+/-0.1 cm for girls) and FF (42.5+/-0.1 cm for boys, 41.5+/-0.1 cm for girls) were well below those of BF group (43.7+/-0.1 cm and 42.9+/-0.1 cm for boys and girls, respectively) and the standard curve (P < 0.05). These results suggest that exclusive breast feeding is sufficient during the first 6 months, the most important period of life. (C) 1997 Elsevier Science B.V.