The influence of methanol on the activity, stability and internal dynamics of myoglobin (Mb) has been investigated to obtain information about the effect of alcohol on protein behaviour. Spectroscopic investigations show that there are no significant changes in conformational structures of the protein within the range of alcohol concentrations where the catalytic activity (k(cat)) and thermal stability (T-m) of Mb decrease. Neutron scattering measurements indicate that the characteristic times related to protein internal fluctuations increase when the methanol molar fraction in the mixtures increases. This suggests a direct relationship between the protein internal motion rate and the catalytic activity. (C) 2009 Elsevier B. V. All rights reserved.