Women with palpable breast cysts which are lined with apocrine epithelium may be at higher risk of developing breast cancer than women with breast cysts which are lined with flattened epithelium, the former group being characterized by intracystic sodium to potassium ratios below 3, while the latter group has intracystic sodium to potassium ratios above 3. In this study the distribution of intracystic concentrations of the mitogenic peptides, epidermal growth factor, endothelin and gastrin‐releasing peptide in the 2 groups of breast cysts were compared to see whether differences in concentrations between the 2 cyst groups might provide an explanation for the higher risk of breast cancer observed in women with “apocrine” breast cysts. The concentrations of epidermal growth factor and gastrin‐releasing peptide were significantly higher in the low electrolyte ratio group (p < 0.001). There was no difference in endothelin concentrations between the 2 groups. Negative correlations were found between epidermal growth factor concentrations and Na+/K+ and between gastrin‐releasing peptide concentrations and Na+/K+ (p < 0.001). A positive correlation was found between gastrin‐releasing peptide and epidermal growth factor concentrations in breast cyst fluid (p < 0.001). The significantly higher intracystic concentrations of both epidermal growth factor and gastrin‐releasing peptide in the low‐electrolyte‐ratio group may provide an explanation for the higher risk of breast cancer which has been observed in women with “apocrine” breast cysts.