An absolute kinetic scale for amidyl radical reactions was established by a combination of direct laser flash photolysis (LFP) and indirect competition-kinetic studies. Six amidyl radicals were studied by LFP. Arrhenius parameters were determined for 6-exo cyclizations of the N-butyl-6,6-diphenyl-5-hexenamidyl radical (2) and the N-butyl-6-(trans-2-phenylcyclopropyl)-5-hexenamidyl radical (5) and for 1,5-hydrogen transfer in the N-(6,6-diphenyl-5-hexenyl)acetamidyl radical (3); rate constants for these reactions at 20 degrees C are 3.0 x 10(7) s(-1) (2), 5.5 x 10(6) s(-1) (3), and 1 x 107 s(-1) (5). Kinetic limits were established by LFP for the fast cyclizations of the N-methyl-5,5-diphenyl-4-pentenamidyl radical (1) and the N-methyl-5 -(trans-2-phenylcyclopropyl)-4-pentenamidyl radical (4) (k > 2 x 10(8) s(-1) at ambient temperature) and for the slow fragmentation of the N-(2,2-diphenylethyl)acetamidyl radical (6) (k = 2 x 10(4) s(-1) at 48 degrees C). Rate constants for amidyl radical reactions with Bu3SnH and PhSH were determined by competition kinetics; respective rate constants are 1.3 x 10(9) M-1 s(-1) at 20 degrees C and 9 x 10(7) M-1 s(-1) at 23 degrees C. Cyclizations of simple amidyl radicals were determined from competition kinetic studies by employing Bu3SnH and N-(phenylthio)amide radical precursors using data from the literature and from studies in this work. Rate constants ac 65 degrees C for 5-exo cyclizations of the N-butyl-4-pentenamidyl radical and the N-(4-pentenyl)butanamidyl radical and for 6-exo cyclization of the N-ethyl-5-hexenamidyl radical are 3 x 10(9) s(-1), 7 x 10(8) s(-1), and 1.0 x 10(7) s(-1), respectively. The kinetic values determined in-this work can be employed in synthetic planning involving amidyl radicals, and the simple amidyl radical clocks can be used for measuring rate constants of bimolecular reactions. A compilation of the kinetics of nitrogen-centered radical cyclizations and bimolecular reactions of nitrogen radicals with Bu3SnH and PhSH is presented.