Feasibility study of two-layered dissolving microneedles for percutaneous delivery of peptide/proteins using recombinant human growth hormone (rhGH) and desmopressin (DDAVP). Two-layered dissolving microneedles were administered percutaneously to the rat skin. Plasma rhGH and DDAVP concentrations were measured by EIA and LC/MS/MS. In vivo dissolution and diffusion rates of drugs in the skin were studied using tracer dyes, lissamine green B (LG) for rhGH and evans blue (EB) for DDAVP. Diffusion of drugs vertically into the skin was studied using FITC-dextran (MW = 20 kDa)-loaded dissolving microneedles. Stability experiments were performed at −80°C and 4°C. The absorption half-lives, t 1/2a, of rhGH and DDAVP from dissolving microneedles were 23.7 ± 4.3–28.9 ± 5.2 and 14.4 ± 2.9–14.1 ± 1.1 min; the extents of bioavailability were 72.8 ± 4.2–89.9 ± 10.0% and 90.0 ± 15.4–93.1 ± 10.3%, respectively. LG and EB disappeared from the administered site within 2 h and 3 h after administration. Five green fluorescein spots were detected at 15 s and enlarged transversally at 30 s. FITC-dextran was delivered into the microcapillaries at 5 min and 10 min. The rhGH and DDAVP were stable in dissolving microneedles for one month at −80°C and 4°C. Results suggest that the two-layered dissolving microneedles are useful as an immediate-release transdermal DDS for peptide/protein drugs.