Leaf-tip appearance and duration from planting to panicle initiation (PI) are important developmental processes in cereals. This study was conducted to determine the effect of air temperature on rates of leaf-tip appearance and 1/PI for sorghum [Sorghum bicolor (L.) Moench]. Nine genotypes were grown in pots at mean temperatures of 17 to 33C and photoperiods of 11.0 to 12.3 h d-1 in glasshouses. Leaf-tip appearance was recorded every 3 to 5 d and PI determined by apical dissection. The optimum temperature (To) for 1/PI was between 26 and 27C and supra-optimal temperatures delayed PI in all genotypes. The base temperature (Tb) ranged from 6 to 10C but only one genotype had a Tb significantly different from a common value of 8.5C. Growing degree days (GDD) for PI among genotypes at sub-optimal temperatures varied from 411 to 592 (P 0.001) above a Tb of 8.5C. Warmer temperatures ( 27C) reduced the rate of leaf-tip appearance in five genotypes; in the remaining genotypes the rate of leaf appearance was effectively constant at mean temperatures between 23 and 33C. There was no significant difference (P 0.20) among genotypes in the phyllochron, which was 57 GDD above a Tb of 8.5C. The final number of leaf-tips was constant within genotypes at mean temperatures of 18 to 30C, but varied among genotypes from 11.8 to 17.3. In conclusion, the Tb and To for 1/PI were approximately 8.5 and 27C and there was variation in 1/PI but not in the rate of leaf-tip appearance among the genotypes studied.