Abstract The simultaneous voltammetric determination of adenosine (ADS) and dopamine (DA) using a single wall carbon nanotube (SWCNT) modified glassy carbon electrode (GCE) is reported. This has physiological importance in controlling Parkinson’s disease. In phosphate buffer medium of pH 7.2, the concentration vs. peak current plots were linear in the range 1–100 μM for ADS and DA. A comparison of the voltammetric response of DA at acid-treated (purified and super-purified) and untreated SWCNT modified GCE indicates that the oxidation peak current of DA decreases considerably at the treated SWCNT modified GCE. This indicates that metallic impurities in nanotubes play a large role in enhancing the electrochemical current. The detection limit (3 σ) and sensitivity observed for ADS and DA were 34.7 μM, 7 μM and 9.5 nA μM −1, 77.9 nA μM −1, respectively.