Abstract: Effects of different PH's and deoxygenation were studied on ESR spectra of several piperidine nitroxyl radicals in solutions. Two water-soluble radicals were observed to be considerably stable in buffer solutions with PH_3-12.Deoxy -genation did not affect the ESR characteristics of free radicals in the solid state, but in their solutions, it was the solvent polarity that played a dicisive role in the emergence of deoxygenation effects. In solvents with lower polarity, deoxygenation led to a marked narrowing and intensification of ESR spectra. And what is more, the degree of perfectness of the ¹⁴N hyperfine splitting became very conspicuously enhanced. However, the deoxygenation effects in aqueous solutions were negligible.