1. In chicken embryo cartilage putrescine levels, maximal at day 8, fall by day 16 to a four-fold lower value, which remains unchanged through hatching and in the 12-day-old chick. 2. Spermine and spermidine, initially higher than putrescine, are almost halved between days 8 and 11, and remain constant afterwards. 3. Ornithine decarboxylase is down to 20% of the day 8 value by day 16, and is further reduced in the newly hatched chick. 4. S-Adenosyl-methionine decarboxylase activity shows a 50% reduction between days 8 and 11, and no further changes. 5. Spermidine acetyltransferase activity at day 11 is 30% lower than at day 8, goes back up to the initial level by day 16, and progressively decreases through hatching and the first 12 days of life.