We have used the fluorescence-dip technique to obtain double-resonance spectra of transition-metal atoms producedin a rf glow-discharge sputtering machine. Rydberg spectra of the neutral elements Ti, V, Fe, Co, and Ni have been analyzed to yield ionization potentials accurate to 1 cm, completing the table of values for the iron period (K through Zn). The 63 737-cm- value obtained for Fe agrees with a recently reported result, and new ionization potentials for Ti, V, Co, and Ni are 55073, 54413, 63 565 and 61619 cm', respectively. Quantum defects for nd and ns series were obtained. Series converging to some excited ion core levels do not show detectable s-d mixing, which would provide a directionization channel and lead to the asymmetric line shapes that are characteristic of autoionization. Fano q parameters were determined for states autoionizing without a change incore configuration. Resolved spectra of low-lying Rydberg states display a complicated level structure not observed in studies of alkali or rare-gas atoms. © 1990 Optical Society of America.