Reductions of the protein myoglobin reconstituted with cobalt(III) heme [MbCo(III)] were accomplished in liquid crystal films of didodecyldimethylammonium bromide (DDAB) on pyrolytic graphite (PG) electrodes in pH 7 buffer. Slow electron transfer to MbCo(III) was detected by square wave voltammetry, and a well-defined, reversible cyclic voltammogram was observed for the MbCo(II)/MbCo(I) redox couple with a formal potential of - 0.85 V versus SCE and 25 mV peak potential separation at 100 mV s(-1). The MbCo(III)/MbCo(II) couple mediated the reduction of oxygen, while the MbCo(II)/MbCo(I) couple mediated the reduction of ethylene dibromide.