Four general zones of f-actin movement are seen in primary cultures of newt lung epithelial cells microinjected with X-rhodamine actin. At the leading edge and throughout the lamellipodium, f-actin speckles continuously appeared and moved towards the cell center. As speckles approached the junction between the lamellipodium and lamellum they usually disappeared, F-actin underwent slower retrograde flow in the lamellum, and F-actin generally moved forward in the cell body. Time-lapse FSM was performed on a spinning disk confocal microscope system. Light from a 50 mW Krypton-Argon ion laser (Melles Griot, OmniChrome) was delivered by a single-mode fiber optic (Point Source) to a Yokogawa spinning disk confocal scan-head (Ultra-View; PerkinElmer) on an inverted microscope (TE300 Quantum; Nikon). Images were collected by a 100x 1.4NA Plan-Apo DIC objective lens (Nikon) and captured with an Orca 2 camera (Hamamatsu). Images were collected in the ventral focal plane at 10 s intervals. Images were processed as follows: (1) background subtraction; (2) 3 x3 low pass filter; (3) unsharp mask filter. Corresponds to Fig 2E and video 2 in JCB , Volume 158, Number 1, July 8, 2002 31-37