Iron(III) protoporphyrin IX (Fe(III)P), adsorbed either on single-walled carbon nanotubes (SWCNT) or on hydroxyl-functionalized SWCNT (SWCNT-OH), was incorporated within a Nation matrix immobilized on the surface of a graphite electrode. From cyclic voltammetric measurements, performed under different experimental conditions (pH and potential scan rate), it was established that the Fe(III)P/Fe(II)P redox couple involves le(-)/1H(+). The heterogeneous electron transfer process occurred faster when Fe(III)P was adsorbed on SWCNT-OH (similar to 11 s(-1)) than on SWCNT (similar to 4.9 s(-1)). Both the SWCNT-Fe(III)P- and SWCNT-OH-Fe(III)P-modified graphite electrodes exhibit electrocatalytic activity for H2O2 and nitrite reduction. The modified electrodes sensitivities were found varying in the following sequences: SSWCNT-OH-F(III)P = 2.45 mA/M approximate to SSWCNT-F(III)P = 2.95mA/M > S-Fe(III)P = 1.34 mA/M for H2O2, and SSWCNT-F(III)P = 3.54 mA/M > S-Fe(III)P = 1.44 mA/M > SSWCNT-OH-Fe(III)P = 0.81 mA/M for NO2-. (c) 2006 Elsevier Ltd. All rights reserved.