Many similarities exist between the inhibitory influence of estrogen on food intake (FI) and body weight (BWt) in female rats and the effect of lateral hypothalamic (LH) lesions on energy balance. Thus, a possible interaction of small electrolytic LH lesions (0.8 mA/10 sec) with hormone-dependent changes in FI, BWt and feeding patterns of female rats was examined. Relative to sham operated controls, rats with LH lesions showed a transitory period of anorexia and initial loss of BWt. Subsequently, FI and BWt gains of lesioned rats returned to control levels although a small chronic reduction in mean BWt was observed relative to sham animals. Daily changes in FI and BWt during 4-day estrous cycles as well as post-ovariectomy increases in FI and BWt were comparable for lesion and sham animals. Also, both groups showed a similar decrease in FI and BWt following a SC injection of estradiol benzoate (EB). Possible effects of LH lesions were further examined by analyzing feeding patterns. Feeding behavior was continuously monitored with photodetectors and recorded on an Esterline Angus event marker before and after a single SC injection of 6 micrograms of EB. Relative to shams, LH animals showed an exaggerated diurnal distribution of meals, ate smaller meals of shorter duration and had larger intervals between meals during the light period. EB was found to shift the feeding patterns of sham animals towards the meal patterns shown by the lesioned rats (exaggerated diurnal distribution of meals, etc.). However, the lesioned rats also showed a normal change in feeding patterns following EB, albeit these changes occurred from a markedly different baseline level.(ABSTRACT TRUNCATED AT 250 WORDS)