In recent years, insight into the role of unique immune molecules in preventing infections has been gleaned from the study of patients with recurrent single-agent infections, and the IL-17 pathway is gaining particular attention. This month, Maria-Luisa Alegre and Jonathan Bromberg discuss three recent papers that strongly link a defect in the IL-17 pathway to chronic mucocutaneous candidiasis, a condition thought to be controlled by the adaptive immune system, in contrast to the neutrophil requirement for prevention of invasive candidiasis.