A 3-year-old boy who presented with flaccid weakness of the right lower limb 1 week after treatment for an acute attack of asthma is described, Sensation was normal. Electromyography suggested anterior horn cell damage and persisting weakness. These features suggested a diagnosis of Hopkins syndrome. Complement fixation test titer and agglutination test titer to Mycoplasma pneumoniae were significantly increased, suggesting a previously unreported association with this syndrome, We review possible infectious agents detected in previous reports. (C) 1997 by Elsevier Science Inc.