Three quaternary sulfides ACuMnS(2) (A = K, Rb, Cs) with the ThCr2Si2-type structure were prepared from alkali metal carbonate A(2)CO(3), MnS, and CuO by CS2/N-2 sulfurization. The samples are degenerate semiconductors (rho(RT) similar to 10(-1) Omega.cm). In the temperature range 100-300 K, the susceptibility of all the samples shows a weak maximum consistent with localized antiferromagnetic exchange in isolated two-dimensional manganese cluster nets. The divergence of the FC and ZFC molar susceptibilities (chi(FC) > chi(ZFC)) for all the samples suggests spin-glass-type behavior with a well-defined freezing temperature, T-f of approximate to 35 K.