The triplet state properties of 7-azatryptophan (7AW), 5-hydroxytryptophan (5HW), and the 5HW anion (pH ) 12.3) have been investigated by optically detected magnetic resonance, ODMR, in zero applied field. Also the triplet state properties of tryptophan (Trp) have been reexamined. Analysis of "slow-passage" ODMR responses during phosphorescence decay (delayed ODMR) that contain the effects of fast passage is introduced using Marquardt-Levenberg nonlinear least-squares fitting. The parameters determined by the analysis of delayed ODMR are the band center frequency (ν 0 ) and bandwidth (ν 1/2 ) of the inhomogeneously broadened ODMR band, the apparent decay constants of the triplet sublevels, and their relative radiative rate constants. The values of ν 0 and ν 1/2 are obtained with greater accuracy than is possible with analysis that does not account for fast passage effects on the band shape. The kinetic parameters are influenced somewhat by residual spin-lattice relaxation (SLR) effects, however. The zero-field magnetic resonance frequencies and band widths have been determined for Trp, 7AW, 5HW, and 5HW anion, along with the apparent kinetic parameters for Trp and 7AW. Microwave-induced delayed phosphorescence transient responses of 5HW and its anion are analyzed globally to give kinetic parameters free of residual effects. The ODMR band widths of 5HW and its anion greatly exceed those of Trp, while those of 7AW are significantly narrower. The zero-field-splitting (ZFS) parameter E is reduced in 5HW and its anion to about half its value in Trp, while the E-parameter of 7AW increases by about 10%. Sublevel decay constants relative to Trp are hardly changed in 5HW, but increase significantly in the anion. Decay constants of Trp increase moderately with 7-aza substitution, as expected from introduction of spin-orbit coupling at the N atom. The pattern of ODMR bandwidths of Trp and 7AW is consistent with a positive correlation of solvent induced shifts in the ZFS Dand E-parameters.