Homozygotes raised at 16^oC are lethal, at 20^oC are rudimentary and at 25^oC are wild type in phenotype; the same results are observed in r^CS1/Df(1)r-D17 and r^CS1/r¹ heterozygotes; r¹ is deficient for DHO only. Heterozygotes with r¹¹, which is deficient for CPS, are rudimentary at all temperatures and heterozygotes with r^53l and r^56j, which lack ATC activity, are wild type at all temperatures. Cold-sensitive periods during embryogenesis and during organogenesis in the early pupal stage; larval stages cold stable. Activities of DHO isolated from early embryos cold-sensitive; CPS exhibits reduced activity at all temperatures; ATC cold stable.