Optogalvanic laser spectroscopy has been applied to measure the hyperfine structure of 12 spectral lines of Mn I in the wavelength regions of 660-645 nm and 933-911 nm. Experimental hyperfine structure constants A and B of the isotope(55) Mn have been determined for seven levels of even and seven levels of odd parity. Additionally, a parametric analysis of the fine structure and the magnetic dipole hyperfine structure has been performed for the three even configurations 3d(5)4s(2), 3d(6)4s and 3d(7). Very large values for the ratio a(3d)(10)/a(3d)(01) are found. Theoretical predictions for the magnetic dipole hyperfine structure constants A for all levels of the configurations 3d(5)4s(2) 3d(6)4s and 3d(7) are given.