Five members of an elicitor-like gene family from Phytophthora infestans were examined. The family was first identified by analyzing mating-induced gene M81, which resembled a 42-kDa P. sojae glycoprotein known to elicit defense reactions in plants including the host of P. infestans, potato. M81 was the most structurally and functionally diverged of the P. infestans genes compared to the P. sojae sequence. M81 lacked elicitor activity, had the lowest protein identity (47%), displayed mating-specific transcription, and had a novel C-terminal domain. The latter contained a 30 residue proline/threonine-rich motif, tandemly repeated 24 to 36 times depending on the allele. M81C, M81D, and M81E better resembled the P. sojae protein based on amino acid identity (63 to 75%) and conserved elicitor activity. M81C and M81D were transcribed only during zoosporogenesis while M81E expression was restricted to hyphae. M81B was physically linked to M81 and appeared to be a pseudogene. The protein products of each gene, which were sized from 436 to 1607-amino acids, were predicted to be extracellular transglutaminases. Genes with elicitor, proline/threonine-rich repeat, and both elicitor and repeat domains were widely distributed throughout Phytophthora. These findings help explain the natural functions of elicitors in pathogen biology and plant-microbe interactions.