Protein transporters move essential metabolites across membranes in all living organisms. Downy mildew causing plant pathogens are biotrophic oomycetes that transport essential nutrients from their hosts to grow. Little is known about the functions and gene expression levels of membrane transporters produced by downy mildew causing pathogens during infection of their hosts. Approximately 170–190 nonredundant transporter genes were identified in the genomes ofPeronospora belbahrii,Peronospora effusa, andPeronospora tabacina, which are specialized pathogens of basil, spinach, and tobacco, respectively. The largest groups of transporter genes in each species belonged to the major facilitator superfamily, mitochondrial carriers (MC), and the drug/metabolite transporter group. Gene expression of putativePeronosporatransporters was measured using RNA sequencing data at two time points following inoculation onto leaves of their hosts. There were 16 transporter genes, seven of which were MCs, expressed in eachPeronosporaspecies that were among the top 45 most highly expressed transporter genes 5–7 days after inoculation. Gene transcripts encoding the ADP/ATP translocase and the mitochondrial phosphate carrier protein were the most abundant mRNAs detected in eachPeronosporaspecies. This study found a number ofPeronosporagenes that are likely critical for pathogenesis and which might serve as future targets for control of these devastating plant pathogens.