Summary On the second day of imbibition in germinating seeds of Impatiens balsamina - when hypocotyl and root growth starts - phenylpropanoid compounds begin to accumulate, whim arc different from those in dry seeds (sec WEISSENBOCK and REZNIK, 1970). This accumulation occurs in light and in darkness. Correspondingly a low PAL-activity is measurable at this time. This activity increases steeply in both illuminated and etiolated seedlings in the following days; it reames a maximum on the 4th day of germination, which is about 1,5 times greater in seedlings in the light than in those in the dark (fig. 1 a, 2 a) . Subsequently PAL-activity decreases again, in the light slightly faster than in darkness, until a relatively stable level is reached on the 6th to 7th day. In seedling germinating in continuous white light there is a direct correlation between PAL-activity and the synthesis of derivatives of cinnamic acids and flavonol glycosides up to the 4th day when the rate of synthesis reaches its maximum. This production of fIavonoids continues at the time when enzyme activit y has passed its maximum (fig. 1 a, b). In contrast etiolated seedlings show - despite of a reasonable PAL-activity - a relatively small increase in the amount of cinnamic acid esters during the first 4 days and a decrease in those compounds when the activity of this enzyme has passed its maximum. In these seedlings the newly formed flavonois arc present in trace amounts in the beginning, they accumulate only slightly in later developmental stages (fig. 2 a, b). In both, light- and dark-grown seed lings an unknown substance (10), exhibiting a violet blue fluorescence accumulates.