The relationship between intracystic levels of epidermal growth factor (EGF) and those of dehydroepiandrosterone sulphate (DHEA-S), delta-4-androstenedione (delta-4-A), 17-beta-estradiol (17-beta-E) and progesterone (PROG) have been studied in 77 breast cyst fluid (BCF) samples. EGF and all tested hormones appeared to be inversely correlated with the intracystic Na+/K+ ratio (p less than 0.001). Consequently, when the BCFs were subdivided according to the Na+/K+ ratio, significantly higher levels of EGF, DHEA-S, delta-4-A, 17-beta-E and PROG were found in Na+/K+ less than 3 BCFs compared with Na+/K+ greater than 3 BCFs (p less than 0.001 in all cases). Strong direct relationships were found among all steroid hormones when they were correlated to one another (p less than 0.001). Intracystic EGF concentration was directly and significantly correlated with each tested hormone (p less than 0.001). However, the relationship between EGF and steroid hormones appeared to be different in the 2 BCF types (Na+/K+ less than 3 or greater than 3).