A series of homologs of idoxifene [1a, (E)-1-[4-(N-pyrrolidinoethoxy)phenyl]-1-(4-iodophenyl)-2-phenyl-1-butene] and selected homologs of 4-iodotamoxifen [2a, (E)-1-[4-[(N-dimethylamino)ethoxy]phenyl]-1-(4-iodophenyl)-2-phenyl-1-butene] with the side chain (CH2)n varying in length from n = 3 (1b, 2b) to n = 10 (1i, 2i) have been synthesized and tested for antagonism of the calmodulin-dependent activity of cAMP phosphodiesterase and for binding affinity to rat uterine estrogen receptor. Compared with 1a (IC50 = 1.5 μM), the homologs showed a progressive increase in calmodulin antagonism with a maximum inhibition at n = 7−9 (1f−h) (IC50 = 0.2 μM), declining at n = 10 (1i) to IC50 = 1.6 μM. In the pyrrolidino series, estrogen receptor binding affinity peaked at n = 3 (1b, RBA = 23; estradiol = 100), declining by n = 10 (1i) to RBA = 0.4, but the homolog n = 8 (1g, RBA = 3.5) was still comparable to tamoxifen (RBA = 3.9). A similar pattern of activity was seen for the dimethylamino counterparts. These compounds represent a new class of antiestrogens with potent calmodulin antagonism.