Lymphocyte migration into fresh and preserved peripheral nerve allografts was assessed to determine the effects of preservation time, preservation temperature, and graft harvest technique on the immunologic response to the peripheral nerve allograft. Peroneal nerve was harvested from either live or cadaveric (tissue) donors and stored as 1.5-cm segments at 5°C or 37°C for 1, 3, 5, or 7 days. Each of nine outbred ewes then received multiple segments of peroneal autograft, fresh allografts, and preserved nerve allograft implants. Lymphocyte migration was studied 7 days after implantation by intravenous injection of autologous 111In-labeled lymphocytes and quantified by gamma counter. Lymphocyte migration into fresh allografts (7212 ± 1575) increased an average of 4.1 times over fresh autograft tissue (1758 ± 421; p < 0.05). Short-term preservation (24 hours) at both temperatures enhanced lymphocyte migration into pretreated allograft tissue (12681 ± 2575 at 5°C, 8751 ± 1577 at 37°C) as compared with fresh allograft (7212 ± 1575). Conversely, 7 days of pretreatment at both 5°C (3586 ± 1421) and 37°C (1570 ± 414) resulted in migration values not significantly different from autograft. No statistically significant difference was seen between grafts harvested from live (5710 ± 1651) versus cadaveric (tissue) donors (4013 ± 832) after 5 days of cold preservation.