My daughter had bathtub fear starting around 7 months... she had been in one of those meshy bathseat bathers and she loved it. In the seat, her butt didn't actually sit in the water. Then all of the sudden she hated it. We tried a couple things, but ultimately what worked for us was her sitting on a bath mat in the tub and she has a lot of toys to play with. We have these rubber duckies that have lights in them and when they hit the water, they light up. She LOVES them!
Maybe you can try to ease the baby into the tub... like go into the bathroom and sit outside of the tub, and splash around with your hands a bit to show how fun it is. Then get a tubby toy and give it him to play with outside of the tub, then put it in the tub and maybe he'll go for it.
Hope this helps! Good luck!
at 2:10 PM on Jan. 25, 2009