XEs cause PRL release, and XE mixtures alter these responses. We measured PRL release into the culture medium by RIA after a 1-min exposure to (A) individual XEs (10-15 M – 10-7 M) and also as (B) XE mixtures (10-15 M – 10-7 M) with a constant physiologic E2 concentration (10-9 M) throughout the dose-response range of the XEs. The amount of PRL secreted for each well was normalized to the CV value for cell number, and expressed as a percentage of vehicle (V)-treated controls. Error bars are means ± S.E. For positive (E2) and negative (V) controls, the width of the bars indicate error ranges (V ±1.5; 10-9 M E2 ± 1.6). n = 24 over 3 experiments. * = p < 0.05 compared to vehicle; in B, # = p < 0.05 compared to 10-9 M E2. The E2 (10-9 M) response is significantly different compared to the vehicle control.