Effect of pre-incubation of cells with 50 μM of estrogen antagonist ICI-182,780 for 2-h on the stimulation of AA release by tamoxifen. The cells were pre-incubated for 2-h with 50 μM ICI-182,780. The data recorded are the sum of the AA released during the 2-h pre-incubation plus the average of the subsequent 6-h incubation. During the 2-h pre-incubation, 3.1 ± 0.02(4) and 2.6 ± 0.26(4) % AA was released by the control MEM/BSA and MEM/BSA containing ICI-182,780 respectively. (□) = MEM/BSA; (■) = MEM/BSA containing 16 μM tamoxifen. Each bar gives the mean value and the brackets give the SEM.