Measles (rubeola) is still important, even though widespread vaccination has begun. Measles is spread by droplet inhalation. Incubation lasts about 9-11 days, followed by 3-4 days of fever, cough, and sometimes conjuctivitis. Koplik’s spots appear on the oral mucosa in 50%-90% of patients about 2-3 days after symptoms begin. These last about 6-7 days. The typical measles skin rash begins about 4-5 days after onset of upper respiratory tract symptoms. The two main complications are encephalitis and pneumonia. Fortunately, encephalitis is rare, the incidence being 0.01%-0.2%. Due to the great frequency of the disease, however, the total number of cases is appreciable. About one third of those with encephalitis die, one third recover completely, and the remainder survive but show moderate to severe residua. Measles encephalitis is considered postinfectious because it develops 4-21 days after the onset of rash. Measles involves lymphoid tissue and respiratory epithelium early in the illness. Therefore, bronchitis, bronchiolitis, and pneumonia are fairly frequent. Most cases of pneumonia are due to superimposed bacterial infection (staphylococci, pneumococci, streptococci), but some are caused directly by the rubeola virus. Secondary bacterial otitis media is also fairly frequent. For diagnosis, culture and serologic tests are available. Standard culture takes 7-10 days. Culture depends on the stage of disease. For a period of 1 week ending with the first appearance of the rash, blood, nasopharyngeal swabs, or urine provide adequate specimens. After appearance of the rash, urine culture is possible up to 4 days. Beyond this, culture is not useful, and serologic tests must be employed using acute and convalescent serum specimens. Measles HI-detectable antibodies appear about the end of the first week after appearance of the rash and peak about 2 weeks later. Measles IgM antibody appears about 2 days following rash onset, peaks about 10-14 days after rash onset, and becomes undetectable at about 30 days. Interpretation is similar to that of rubella tests. However, one report indicates about 30% false negative IgM results even 3 weeks after disease onset. IgG acute and convalescent serum specimens can also provide a diagnosis.