Abstract: The present invention provides 4-[1-Aryl-imidazol-4-ylethynyl]-2-alkyl-pyridine and 1-heteroaryl-imidazol-4-ylethynyl]-2-alkyl-pyridine derivatives and pharmaceutically acceptable salts thereof for the treatment or prevention of disorders mediated in full or in part by metabotropic glutamate receptor 5. These disorders include, e.g. acute, traumatic and chronic degenerative processes of the nervous system, such as Alzheimer's disease, senile dementia, Parkinson's disease, Huntington's chorea, amyotrophic lateral sclerosis and multiple sclerosis, psychiatric diseases, such as schizophrenia and anxiety, depression, pain and drug dependency.