Because women are exposed to environmental estrogens during life phases when different physiologic estrogens are prevalent, we studied the changes in pERK when each physiologic and environmental estrogen was present simultaneously. We previously detailed ERK (and other) responses of these cells to the physiologic estrogens E 1 , E 2 , and E 3 ( Watson et al. 2008 ); those data can be directly compared with results of the present study. First, we examined the time-dependent changes in ERKs ( Figures 1 – 3 ), showing that estrogenic stimulation caused a characteristic oscillating pattern with immediate (5 min), intermediate (10–30 min), and long-term (after 30 min) rises in ERK activation, similar to estrogen-induced fluctuations we reported previously ( Bulayeva et al. 2004 ; Bulayeva and Watson 2004 ; Jeng et al. 2009 ; Jeng and Watson 2009 ; Kochukov et al. 2009 ; Zivadinovic and Watson 2005 ). We observed these oscillating patterns for all estrogens, although some were “trends” with peaks that did not achieve significance. The physiologic estrogens E 2 and E 1 , as well as BPA, tended to cause three oscillations during this 60-min time frame, whereas alkylphenols and E 3 caused only two (missing the intermediate peak).