Single-channel measurements were used to study the cis-trans isomerization of a carbamate bond in gramicidin-ethylenediamine, a derivative of the channel-forming peptide gramicidin. From the temperature dependence of transition rates, Delta H-double dagger values of 64.9 +/- 2.5 and 58.2 +/- 3.0 kJ mol(-1) were calculated for isomerization from the trans and cis states, respectively. The entropies of activation were calculated to be near zero as expected for a unimolecular isomerization process. This represents the first characterization of thermal isomerization at the single molecule level. The calculated activation parameters are in very good agreement with previous NMR studies of cis-trans isomerization of carbamate bonds in small molecules. This correspondence validates the use of ion channel measurements for the study of conformational changes at the single molecule level.