Surfactant protein A (SP-A) was modified by covalent linkage with polylysine of average M(r) 21 kD ([Lys]21kD-SP-A) and utilized to transfect human airway epithelial cells (H441) in vitro. Transfection of H441 cells was more efficient with [Lys]21kD-SP-A than with polylysine-DNA or unmodified SP-A-DNA complexes. Transfection with [Lys]21kD-SP-A was effective at a protein-to-DNA molar ratio of 400:1 and in the presence of an exogenous surfactant preparation, Survanta. Transfection with [Lys]21kD-SP-A was reduced in the presence of unmodified SP-A consistent with the concept of a receptor mediated uptake of protein-DNA complexes. Increased transfection efficiency correlated with decreasing diameter of the [Lys]21kD-SP-A-DNA complexes, and these complexes bound to the cell surface and pseudopodia of H441 cells. Transfection was enhanced by co-incubation with replication-deficient adenovirus. Cotransfection by [Lys]21kD-SP-A-DNA and [Lys]10kD-SP-B resulted in an additive level of reporter gene (CAT) expression. [Lys]21kD-SP-A-DNA is likely to be useful as a component of a surfactant-based DNA delivery system for transfection of airway cells.