We have studied the stability and transdermal flux of prostaglandin E₁ (PGE₁) from various donor solutions through hairless mouse skin. Stability in HEPES buffer or in propylene glycol (PG) solution where enhancer (oleic acid (OA), propylene glycol monolaurate (PGML), transcutol (TC), ethanol (EtOH)) is dissolved was investigated. PGE₁ was not stable in HEPES buffer. The concentration of PGE₁ decreased continuously for 7 days, and the degradation rate constant was 0.0028 h^(-1), assuming first order reaction. The effect of current or penetration enhancer on the degradation was minimal. Percutaneous transport from HEPES buffer by passive or iontophoretic delivery without enhancer was close to nil. When OA or PGML was used together with PG, both passive and iontophoretic flux increased. PGML showed better enhancing effect than OA. Flux by cathodal delivery was about 2 times larger than that by passive delivery. Flux by anodal delivery was lower than that by passive delivery. TC and EtOH also increased the transdermal flux, but the effect was not as good as that observed when OA or PGML was used. These stability and flux data provide important information on how to formulate the patch, which will be the next step of this work, and on the polarity of current to use during iontophoresis.