We report Vickers microhardness measurements on flux grown single crystals of the YbAg(x)ln(1-x)Cu(4) alloy system. Although sample dependent, the microhardness exhibits a clear concentration dependence: in general, it decreases with x. The lattice parameter as a function of x exhibits a similar behavior. For x < 0.5, where the lattice parameter is almost constant, the microhardness exhibits a weak enhancement. Similar concentration dependence of the lattice parameter, resistivity and microhardness allows us to conclude that the microhardness reflects the evolution of the YbAg(x)ln(1-x)Cu(4) alloy system towards more metallic character with increasing x. (c) 2005 Springer Science + Business Media, Inc.