Pedicle skin flaps have been raised from pre-irradiated sites on the flanks of pigs. Radiation treatment was given as a single dose, 6 fractions in 18 days or 30 fractions in 39 days. Surgery was performed at 12, 52 or 104 weeks after irradiation. Control flaps were raised from normal skin on the other flank. The length of flap remaining viable after surgery was shorter in the irradiated than the control flaps. This reduction in flap survival was the same at the three time periods at which it was assessed and for each of the radiation doses selected for the different treatment groups. Clearance rates of an isotope (99mTechnetium) injected intradermally in the distal surviving regions of irradiated and normal flaps were compared. Clearance changes were related to those recorded in normal and irradiated skin before surgery. Isotope clearance in normal flaps was impaired after surgery (days 1-3) but then became faster than in intact skin (days 5-14). A similar pattern of changes was recorded in irradiated flaps only when the pre-operative isotope clearance rates in irradiated skin were similar to that in normal skin (i.e. for all treatment groups at 52 and 104 weeks after treatment). However, when pre-operative clearance was already slower in irradiated than in normal skin (i.e. for a single dose and 6 fraction/18 days after 12 weeks), surgery in the irradiated site did not have the usual effect of slowing the clearance rate.