A nanosecond laser near-infrared spectrometer was used to study singlet oxygen (O-1(2)) emission in a protein matrix. Myoglobin in which the intact heme is substituted by Zn-protoporphyrin IX (ZnPP) was employed. Every collision of ground state molecular oxygen with ZnPP in the excited triplet state results in O-1(2) generation within the protein matrix. The quantum yield of O-1(2) generation was found to be equal to 0.9 +/- 0.1. On the average, six from every 10 O-1(2) molecules succeed in escaping from the protein matrix into the solvent. A kinetic model for O-1(2) generation within the protein matrix and for a subsequent O-1(2) deactivation was introduced and discussed. Rate constants for radiative and nonradiative O-1(2) deactivation within the protein were determined. The first-order radiative rate constant for O-1(2) deactivation within the protein was found to be 8.1 +/- 1.3 times larger than the one in aqueous solutions, indicating the strong influence of the protein matrix on the radiative O-1(2) deactivation. Collisions of singlet oxygen with each protein amino acid and ZnPP were assumed to contribute independently to the observed radiative as well as nonradiative rate constants.