Adjuvant treatment increases the size of hyperplastic mammary lesions 15 days following neu infusion and results in localized lymphadenopathy. Rats were given 0.5 ml/kg body weight CFA at 5 weeks of age and booster injections IFA at 7 and 9 weeks of age (n = 21). Controls received saline (n = 20). Infusion of the neu oncogene retroviral vector into the fourth mammary gland was done at 8 weeks of age. A. H&E staining of a representative hyperplastic mammary lesion (100× magnification). B. Average lesion area determined for each treatment (n = 179 lesions from controls and 258 from adjuvant-treated rats). C. Total lesion area per gland, normalized to individual mammary gland area (n = 20–21/group). D. Average area of the intramammary lymph nodes from infused glands (n = 20–21/group). Error bars represent +1 SD. *P < 0.001; **P < 0.01, t test.