(a) Phototaxis in C. elegans required ciliary sensory neurons. Laser ablation of a group of ciliary sensory neurons led to a severe defect in light-induced avoidance responses. A 2-s light pulse (UV-A, −1.43log I/Io) was used. **P < 0.0002 compared with mock, n ≥ 4. Error bars represent s.e.m. (b) Phototaxis in C. elegans requires CNG channels. Mutations in the CNG channel homolog TAX-2 led to a severe defect in light-induced avoidance responses. Two different tax-2 mutant alleles (p671 and p691) were examined. Full-length rescue experiments were performed on tax-2(p691) mutant worms expressing a full length tax-2 genomic DNA described previously17. **P < 0.000001 compared with wild type, n = 10. Error bars represent s.e.m. (c) Cell-specific rescue of tax-2 mutant phenotype indicated that CNG channels may act in ciliary sensory neurons to mediate phototaxis. The wild-type tax-2 cDNA was expressed as a transgene in ASJ, AWB or ASK of tax-2 mutant worms using cell-specific promoters (ASJ rescue, n = 10; ASK rescue, AWB rescue and tax-2 mutants, n ≥ 30). **P < 0.004 and *P < 0.04 compared with tax-2(p671). Error bars represent s.e.m.