We only stayed on soy for about 10 days before making the decision that it hadn't made a lick of difference, and got straight onto the Nutramigen. It really does taste nasty and will take a while for your LO to drink it, so all the more reason to start with it as soon as possible. Start making his normal sized bottles but use once scoop of Nutramigen in place of one of the scoops of soy. (So if making 6 ounce bottles, use 6oz water, one scoop Nutramigen and five scoops soy). After 3 days, increase that to two scoops Nutramigen, etc. The more Nutramigen you get into the bottle, the longer it may take him to drink it. I remember it only took 2 days before we moved up to 2 scoops, then 3 or 4 days from there on, but when we were on just one scoop left of soy it took DS a LONG time, about 10 - 14 days I think, before he would drink it all and I could drop the last scoop of soy. So don't lose heart, just go slowly and patiently and he will eventually get used to the taste.