4-(((4-Cyanophenyl)(4H-1,2,4-triazol-4-yl)amino)methyl)phenyl sulfamate (6a) was the first dual aromatase-sulfatase inhibitor (DASI) reported. Several series of its derivatives with various linker systems between the steroid sulfatase (STS) and the aromatase inhibitory pharmacophores were synthesised and evaluated in JEG-3 cells. The X-ray crystal structures of the aromatase inhibitors, DASI precursors 42d and 60, and DASI 43h were determined. Nearly all derivatives show improved in vitro aromatase inhibition over 6a but decreased STS inhibition. The best aromatase inhibitor is 42e (IC50=0.26 nm) and the best DASI is 43e (IC50 aromatase = 0.45 nm, IC50STS = 1200 nm). SAR for aromatase inhibition shows that compounds containing an olkylene- and thioether-based linker system are more potent than those that are ether-, sulfone-, or sulfonamide-based, and that the length of the linker has a limited effect on aromatase inhibition beyond two methylene units. Compounds 43d-f were studied in vivo (10 mg kg(-1), single, p.o.). The most potent DASI is 43e, which inhibited PMSG-induced plasma estradiol levels by 92% and liver STS activity by 98% 3 h after dosing. These results further strengthen the concept of designing and developing DASIs for potential treatment of hormone-related cancers.