The first ionization potential of neutral atoms is determined from thresholds of laser-induced optical breakdown. Bulk material ablation plasma of aluminum, silver, lead, indium and copper is created in laboratory air with focused, 5-ns pulsed Nd:YAG, 1064 nm IR radiation. At fixed spot size of 2 ± 0.1 mm, the laser fluence is varied from 16 to 3 J/cm2. The first ionization potentials of the lines Al I 396.2, Ag I 520.9, Pb I 405.8 and 406.2, In I 410.2 and Cu I 515.3 nm are measured to amount to 5.9 ± 0.2, 7.6 ± 0.3, 7.4 ± 0.2, 5.8 ± 0.1 and 7.7 ± 0.2 eV, respectively.