The compound 4-amino-5-(4-methyl)-4H-[1,2,4]-triazole-3-thiol [AMT], C3H6N4S, crystallizes in the orthorhombic space group Pca2(1) with cell parameters a = 9.8130(3) angstrom; b = 8.8600(5) angstrom, c = 6.5400(5) angstrom, V = 568.61(6) angstrom(3), and Z = 4. The structure was solved by direct methods using SHELXS-97 and refined using SHELXL- 97. The final residual factor is R1 = 0.0465 for 1726 reflections and 75 parameters. The compound 4-amino-5-(4-chlorophenyl)-4H-[1,2,4]- triazole-3-thiol[ACT], C8H7 ClN4S, crystallizes in the triclinic space group P (1) over bar with cell parameters a = 8.0440(8) angstrom, b = 11.527(1) angstrom, c = 11.7780(7) angstrom, alpha = 66.537(6)degrees, beta = 72.990(6)degrees, gamma = 76.001(3)degrees, V = 948.1(1) angstrom, and Z 4. The structure was solved by direct methods using SHELXS- 97 and refined using SHELXL- 97. The final residual factor is R1 = 0644 for 6805 reflections and 254 parameters.