Bromocalix[4]arene methyl ether serves as a precursor in the synthesis of the title thiocalixarene via the reagent CuSEt. Ethylthiocalix[4]arene methyl ether crystallizes in the monoclinic space group P21/c with a = 20.577(9), b, = 10.722(5), c = 20.315(9) Å, β = 120.46(4)°, and Dc = 1.24 g cm-3 for Z = 4. Refinement based on 1441 observed reflections led to R = 0.080. The configuration of the calixarene lies between the partial cone and the 1,3-altemate conformations. Bromocalix[4]arene methyl ether crystallizes in the triclinic space group PI with a = 12.283(7), b = 17.658(9), c = 18.118(6) Å, α = 90.25(6), β = 105.95(4), γ = 105.11(6)°, and Dc = 1.68 g cm-3 for Z = 4. Refinement based on 3028 observed reflections led to R = 0.083. The unit cell also contains four CHCl3 molecules which exist pairwise enclathrated by six calixarenes. The partial cone conformation of the bromocalixarene is identical to that of ethylthiocalix[4]arene methyl ether. © 1990 Kluwer Academic Publishers.