To the Editor.—Ìý Guanidine hydrochloride is of value in the treatment of the Lambert-Eaton syndrome¹ and botulism.² More recently, it was tried in the treatment of motor neuron disease.³Untoward side effects are frequent and include the following: cholinergic reactions of the gastrointestional (GI) system, paresthesias, skin changes, petechiae, and, with high doses, nervousness, tremors, and ataxia^1,3,4 More serious are the occasional occurrences of bone marrow depression and aplastic anemia^3,4 and probably long-term renal impairment.^5,6 Lambert and Howard⁴ and Henriksson et al⁶ mention one patient with elevation of alkaline phosphatase level and other indicators of hepatic dysfunction, which reverted to a normal level after discontinuation of treatment with the drug. Norris et al³ have treated more than 200 patients with various doses of guanidine. Liver function abnormalities are not mentioned in their study. We describe a patient with the Lambert-Eaton syndrome