The authors have studied the magneto-optical Kerr rotation in more than 200 metallic systems comprising alloys as well as intermetallic compounds of 3d transition metals. For all these materials the crystal structure, the lattice constants, the room temperature magnetization and the room temperature Kerr rotation at two different wavelengths are specified. For several series of ternary compounds, comprising Heusler alloys Ni2 In-type compounds and Cr23C6 type compounds, we determined the saturation moment at 4.2 K. For a number of representative alloys or compounds a study was also made of the wavelength dependence of the complex polar Kerr effect. The values of the Kerr rotation obtained at 633 nm were compared with the corresponding values of the measured magnetization. Systematic trends were observed and have been used to classify metallic systems into systems where the Kerr rotation will not reach values much in excess of 1° and systems where higher values are likely to be found.