Nowadays, most exanthematic diseases for which a vaccine is available affect young adults. A large percentage of these cases prove to be rubella. The aim of this study is to assess the performance of specific IgM and RT-PCR for the diagnosis of rubella infection. Fifty-nine patients with clinically suspected measles or rubella, and with available serum, whole blood, urine and pharyngeal exudate specimens were studied. RT-PCR in pharyngeal exudate was found to be the most effective marker at the start of the disease (mean, 2.5 days). IgM detection yielded a larger percentage of positive results (76.2%), but at a later time (3.7 days).