The effect of dry conditions on the population dynamics of the entomopathogenic nematode (EPN) Steinernema affine was studied for one month in the exceptionally dry period in the summer of 2003 in the oak wood in the vicinity of Ceské Budejovice, Czech Republic. Soil moisture, soil temperature, and the abundance of suitable insect hosts were monitored. The abundance of infective juveniles (IJs) was correlated with soil moisture and both these values were gradually decreasing during the study period and finally rapidly increased at the end of the investigation. During this period there was a decline in the number of insects suitable as hosts for S. affine, but not in numbers of unsuitable insects. We hypothesise that the observed decrease in IJ numbers was probably caused by the persistence of IJs in host cadavers due to low ambient moisture.