In CSS, how do i remove spacing between elements? I have borders, padding and margin set to 0 in everything.?

I have my top navigation bar as an image map, and then a div element with a background image which need to be perfectly aed to each other, the two images need to be visually continuous. With both images as elements they align, but with the div there is a white space in both IE6 and Mozilla. It looks like some sort of vertical padding on the div, but I have all padding/borders/margin set to 0.