The shortening of severed squid giant axons (GAs) in vitro was analyzed using video light microscopy. Axonal shortening occurred in two temporal phases along the length of the GA: a rapid initial phase during the first 3.5 min after severance followed by a slower phase lasting at least 30 min. The rate of shortening was greatest near the cut end and declined with distance from the cut end for at least 30 min after transection. Axonal shortening may help pack injury-induced vesicles [3] which facilitate sealing of the cut end [7] and/or retard the entry of various substances.