The effect of linoleic and linolenic acid on antibody (Ab) responses to SRBC and BSA and on growth performance were studied in pullets of three genetically different laying lines. Pullets were fed one of three diets: a control diet, a linoleic acid-enriched diet, or a linolenic acid enriched-diet. The linoleic and linolenic acid enriched-diets were the control diet enriched with either sunflower oil or linseed oil. Two chicken lines divergently selected for high (H) and low (L) Ab responses to SRBC, and a randombred control (C) line were used. Total Ab responses to SRBC were not affected by diet, but in the H line a tendency for higher IgG titers to SRBC after primary immunization were found when birds were fed the linoleic diet. The humoral response to BSA was significantly affected by a line by immunization by diet interaction. In the H line birds, the linoleic diet significantly enhanced Ab titers to BSA as compared to the normal diet and linolenic acid-enriched diet. The linolenic acid-enriched diet significantly decreased Ab titers to BSA in the C line birds. No dietary effects on the titer to BSA were found in the L line birds. During the first 3 wk of life, the linolenic acid-enriched diet resulted in reduced BW gain of H line birds. After that period, no effects of diet on BW gain was found. It is concluded that modulation of Ab responses of poultry to T cell-dependent antigens by essential fatty acids is affected by genotype. The relationship between magnitude of Ab responsiveness, BW, and essential fatty acids is discussed.