Objective: To test whether the combined application of dexamethasone (DEXA) and 3,5-dimethyl-3′-isopropyl- l-thyronine (DIMIT) induces the synthesis of surfactant protein A (SP-A) mRNA at a higher rate than both substances given alone? Study design: Organoid culture of fetal rat lungs (Wistar rats; day 19 of gestation) was prepared. After 48 h of incubation we added DEXA (10 −5, 10 −7, 10 −8 and 10 −9 mol/l), DIMIT (10 −5, 10 −7 and 10 −9 mol/l) and the combination of DEXA in 10 −8 mol/l with various concentrations of DIMIT. After another 48 h of incubation, northern blot and hybridization with a 32 P -labeled SP-A cDNA probe was performed. One-way-variance-analysis with a Scheffé-test, Levene-test and one-sample- t-test were used for statistical analysis. Results: DEXA alone above 10 −8 mol/l resulted in a significant increase, DIMIT resulted in a decrease of SP-A mRNA induction. Combined application of DIMIT and DEXA resulted in a significant increase compared to the controls. Compared to DEXA alone in 10 −8 mol/l, we found an increased induction, but the data were not significant. Conclusions: The combined application of DEXA and DIMIT shows a higher induction of SP-A mRNA than both drugs given alone.