In view of the known anti-inflammatory activities of interleukin (IL) 10, we investigated whether the administration of recombinant murine IL-10 prolonged corneal graft survival. A major histocompatibility complex mismatched rat model with AO rats as recipients of PVG donor corneas was used. A total of 39 corneal allografts was included in this study and divided into 7 groups for different treatments. Group I (n = 6), II (n = 8), III (n = 6) and IV (n = 7) were injected subconjunctivally with saline (control), 0. 5 ng, 5 ng or 50 ng of IL-10, respectively, on the day of transplantation and then on postoperative days (POD) 2, 4, 6, 8 and 10. Group V (n = 4) and group VI (n = 4) were injected intraperitoneally with saline (control) or 1 microg of IL-10, respectively, on the day before surgery, the day of grafting and then on POD 2, 4 and 6. Finally, group VII (n = 4) was injected with both subconjuctival 5 ng of IL-10 and intraperitoneal 1 microg of IL-10 on the same days as the previous groups. The median days for corneal rejection in the various groups were: group I, 11.3 +/- 0.9; group II, 11.5 +/- 0.9; group III, 11.6 +/- 0.8, and group IV, 10 +/- 1.0. Statistical analysis revealed a trend towards rejection (p = 0.08) in group IV (compared to group I). In groups V and VI, corneal rejection was evident on day 12 and in group VII the median time for rejection was 10.5 +/- 0.8 days. These results indicate that IL-10 treatment does not prolong corneal allograft survival and may even accelerate rejection.