The dauer stage of C. elegans development has been well studied to uncover how environmental signals regulate developmental fates. Dauer formation is regulated by three signalling pathways, which the nuclear hormone receptor DAF-12 integrates. On p. 3237, Ohkura et al. report a new dauer-like mutant, sdf-9,that resembles the daf-12 and daf-9 dauer mutants. By mosaic analysis, the authors show that sdf-9, which encodes a tyrosine phosphatase-like molecule, is expressed in two mysterious cells in the head,XXXL/R, which also express daf-9 and npc-1. (DAF-9 is involved in synthesizing the ligand of DAF-12 and NPC-1 functions in intracellular sterol transport.) Because ablating these cells reproduces the phenotype of the sdf-9 mutant, the authors propose that they might play a key role in metabolizing a steroid hormone ligand for DAF-12 through the functions of DAF-9 and SDF-9.