In situ hybridization (ISH) for the diagnosis of fetal infection with porcine parvovirus (PPV) was compared with immune electron microscopy (IEM) and serology by immunofluorescence (IF) for its sensitivity and its applicability in a routine diagnostic laboratory. The technique was applied to the examination of sections of formalin-fixed paraffin-embedded tissues from 68 fetuses. Fifty-three of these fetuses were diagnosed serologically since they had a crown rump length of more than 17 cm, i.e. they were mature enough to mount a humoral immune response; 38 were positive and 15 negative. Eleven out of 15 smaller fetuses examined for the presence of viral antigen by immune electron microscopy (IEM) were positive and 4 were negative. Heart and lung were found to be the most suitable organs for in situ hybridization. In situ hybridization yielded a positive result in 8 of the 11 IEM positive fetuses and in 33 of the 38 serologically positive fetuses. No signal was detected in any of the 4 IEM or the 13 serologically negative fetuses. Expenses for IEM were estimated to be 179% of the expenses for ISH. Expenses for serology by IF on the other hand were 67% of the expenses for ISH. From this it was concluded that the most efficient way to diagnose a fetal infection with PPV was serology by IF, if possible with samples from several fetuses and that the other techniques, IEM or ISH, ought to be reserved for those cases where no immunocompetent fetuses were available for diagnosis.