Studies of 16 relapses in seven patients receiving treatment for Goodpasture's syndrome showed that intercurrent bacterial infection seemed to be the precipitating event in 13 cases, whereas a rising antibody titre to glomerular basement membrane was responsible in only one. This association between infection and relapse in Goodpasture's syndrome has several implications for the pathogenesis of antibody-mediated tissue damage, and, clearly, more experiments are needed. Whatever the explanation, however, prevention and early diagnosis and treatment of infection in anti-GBM disease are important.