The aim of our study was to investigate serum cGMP level in patients treated with L-DOPA alone and L-DOPA with pergolide mesylate (PM) and to compare the obtained values with age-matched healthy subjects. PD patients treated with L-DOPA or with PM + L-DOPA had significantly higher cGMP levels in serum as compared to control. Moreover, cGMP level was significantly higher after treatment with PM + L-DOPA then L-DOPA alone. We did not observed significant differences in UPDRS scores between both PD groups. Our data suggest that changes in serum cGMP level in PD patients are related with PM + L-DOPA or L-DOPA alone therapy.