In constant light, whole apples (cv. Red Spy) that received alternating 6/25°C treatment accumulated more phenylalanine ammonia-lyase (PAL) and anthocyanin than those receiving constant 25° throughout the course of experiment. The stimulatory effect of low temperature (6°) on the activity of PAL and synthesis of anthocyanin was also observed in the alternating light and dark experiment when low temperature was applied in the dark period. In constant light, the activity of phenylalanine ammonia-lyase inactivating system (PAL-IS) was lower in the apples that had received alternating 6/25° treatment than that in apples that had received constant 25°. When the apples were incubated in constant darkness, no accumulation of PAL and anthocyanin occurred but the level of PAL-IS increased steadily throughout the course of incubation. Nitrogen and potassium deficiency increased PAL accumulation and decreased accumulation of PAL-IS in the leaves of greenhouse-grown apple trees. PAL activity was found to be negatively correlated with activity of PAL-IS. It is therefore concluded that low temperature reduces the level of PAL-IS and increases the accumulation of PAL which in turn increase anthocyanin accumulation in the skin of whole apples, and that nitrogen and potassium deficiencies reduce the level of PAL-IS and hence increase the accumulation of PAL in apple leaves.