The magnetic properties of galvinoxyl (4-[3,5-bis(1,1-dimethylethyl) -4-oxo-2,5-cyclohexadiene-1-ylidenemethyl]-2,6-bis(1,1-dimethyl-ethyl)-phenoxy) and F5PNN (2-pentafluorophenyl-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol -1-oxyl 3-oxide) under pressure are presented. We have found that the structural changes of both compounds can be suppressed by pressurization. The phase transition to a diamagnetic state of galvinoxyl can be suppressed by applied pressure. It has been found that under 7 kbar, the transition is sufficiently suppressed and the ferromagnetic interactions are preserved down to low temperature. The temperature dependence of the paramagnetic susceptibility under 7 kbar obeys the ferromagnetic chain model with 2J/k(B) = 25 K. The room-temperature crystal structure of F5PNN involves a uniform chain, while the low-temperature magnetism can be interpreted by the alternating antiferromagnetic chain model with 2J/k(B) = -5.6 K and alpha = 0.4. We found that under 5 kbar. the low-temperature magnetism obeys the uniform antiferromagnetic chain model with 2J/k(B) = -5.6 K, which is consistent with the room-temperature crystal structure.