A culture medium developed for newly isolated plant and insect mycoplasmas (spiroplasmas) has markedly improved the recovery of Mycoplasma pneumoniae from human clinical materials. This medium (SP-4), in combination with a direct fluorescent antibody test, can improve the recovery and identification of the organism by 30 to 40% over conventional culture procedures. Although these improvements in isolation of the organism may lead to new information on the epidemiology of the disease, the most organism may lead to new information on the epidemiology of the disease, the most rapid diagnosis of clinical M. pneumoniae infections in man is still dependent upon accurate measurement of antibody rises in response to the organism. Recent reports of a number of new serological techniques suggest that further improvements in the serological diagnosis of M. pneumoniae infections are possible.