Persistent human polyomavirus infection is asymptomatic with limited s
tates of virus production in the healthy individual, in immunocompromi
sed patients, however, infection may lead to uncontrolled virus growth
and fatal disease. Predominantly the CNS and in rare cases the urogen
ital tract are affected. During the AIDS epidemic, the number of cases
is steadily increasing, thus dictating the need for an early and fast
differential diagnosis. Virological diagnosis is essentially based on
the detection of virus products in tissue or body fluids. Although se
nsitive and specific diagnostic techniques are available for the diagn
osis of polyomavirus infection, widely accepted standards are not yet
reached. This is in part due to the low number of cases in the past, b
ut also to asymptomatic viral activation in nondiseased patients. Thus
, additional parameters have to be evaluated to provide complementary
tools for differential diagnosis.