Acute allograft rejection (AR) remains a major problem in solid organ transplantation. The pivotal mechanism hinges on alloantigen recognition by recipient T helper (T(h)) cells that differentiate into T(h)1 and T(h)2. This study investigated the association of mRNA levels of the transcription factors T-box expressed in T cells and GATA-binding protein 3 with the development of T(h)1/T(h)2-directed immune responses. We investigated the expression of T-bet and GATA-3 mRNA levels and the protein levels of their marker cytokines interleukin (IL)-2 and IL-4 in orthotopically transplanted rat lungs during AR. We observed a nonsignificant increase in T-bet expression following allografting at days 3 and 5 but there was a significant reduction in GATA-3 expression on day 5 compared with controls. The ratio of T-bet to GATA-3 expression showed a trend to increase at day 3 following allografting reaching significance at 5 days. These changes were associated with a significant increase in the expression of IL-2 over IL-4 on days 3 and 5. This study suggests that T(h)1 responses play a major role during AR in the rat lung, and that this differentiation can be monitored by measuring mRNA levels of T-bet and GATA-3.