Luciferase gene expression by intratracheal administration of LPEI polyplex (N/P = 6) or PEG-b-P[Asp(DET)] polyplex nanomicelle (N/P = 80). Samples of the polyplex and the polyplex nanomicelle were prepared before the administration and left for 1 day. The mice (five mice per group) were anesthetized and the polyplex or the polyplex nanomicelle was administered intratracheally. At 24 hour postadministration, the lung tissues were harvested, homogenized, and measured for luciferase activity (mean ± SEM, N = 5). LPEI, linear poly(ethylenimine); PEG-b-P[Asp(DET)], PEG-b-poly{N-[N-(2-aminoethyl)-2-aminoethyl]aspartamide}.