I've taken 4-AD (test precursor) caps for one cycle base and another with a transdermal application (4derm, you might remember it in a red/white spray bottle)...at a pretty hefty dose too
i made pretty significant gains and know how my body reacts
reference:
http://www.1fast400.com/i49_4-Androstenediol.html
"4-androstenediol (4-AD) is an effective prohormone to testosterone. Naturally found in several tissues of the body, 4-AD is converted to testosterone via the enzyme 3beta-HSD. 4-AD converts to testosterone at a significantly higher rate than other commercially available prohormones (such as androstenedione), and also does not have the weakness of conversion to estrogen and/or DHT prior to conversion to testosterone. This makes 4-AD the best testosterone prohormone on the market."