We describe two patients with lateral amyotrophic sclerosis who, after informed 
consent, received empirical treatment with intravenous cephtriaxone at a dose of 
2 g/24 hours for three weeks, with no positive results. The pharmacokinetics of 
this cephalosporin is analyzed, along with the relationship between motor neuron 
disease, neuroborreliosis and immunoreactivity to Borrelia burgdorferi.