The major agents responsible for atypical pneumonia in children include a wide variety of organisms, one Mycoplasma species, two Chlamydia species, a rickettsia, and one fastidious bacterium. Mycoplasma pneumoniae and C. pneumoniae together may be responsible for over 40% of these infections. Recognition of the role that these agents play in pneumonia is important since many of the diagnostic methods used to detect these organisms are not available in most hospital microbiology laboratories. If you don't look, you won't find. Epidemiologic factors can provide valuable clues, especially with the less frequently encountered infections, since it is almost impossible to make a clinical diagnosis on which to base treatment. A reliable history of avian exposure should suggest psittacosis, exposure to sheep or pregnant cats suggests Q fever, and children with underlying malignancy or immunodeficiency or those receiving systemic steroids may have legionnaires' disease. None of these organisms are susceptible to beta-lactam antibiotics. Sometimes the diagnosis is not considered until after the child has failed to respond to a penicillin or a cephalosporin and routine bacteriology is negative. In view of the role played by M. pneumoniae and C. pneumoniae, a macrolide may be the first-line antibiotic for atypical pneumonia in children.