The oomycete genus Phytophthora includes many of the world's most destructive plant pathogens, which are generally disseminated by asexual sporangia. To identify factors relevant to the biology of these propagules, genes induced in sporangia of the potato late blight pathogen, P. infestans, were isolated using cDNA macroarrays. Of about 1900 genes known to be expressed in sporangia, 61 were up-regulated >5-fold in sporangia versus hyphae, including 17 induced >100-fold. A subset were also activated by starvation and in a non-sporulating mutant. mRNAs of some genes declined in abundance after germination, while others persisted through the germinated zoospore cyst stage. Functions were predicted for about three-quarters of the genes, including potential regulators (protein kinases and phosphatases, transcription factors, G protein subunits), transporters, and metabolic enzymes. Predominant among the latter were several dehydrogenases, especially a highly expressed sorbitol dehydrogenase that accounted for 3% of mRNA. Sorbitol dehydrogenase activity also rose during sporulation and several stress treatments, paralleling the expression of the gene. Another interesting metabolic enzyme resembled creatine kinases, which previously have only been reported in animals and trypanosomes. These results provide insight into the transcriptional and cellular processes occurring in sporangia and identify potential targets for crop protection strategies.