Both bacterial diseases and Early Blight create spots on the leaves... do they have spots, or are they just uniformly yellow? (The "salt damage" picture in the Tomato Problem Solver looks like half a hundred things, and salt is one of the less likely.)

Bacterial diseases progress so slowly that they usually aren't a big problem during the season. Fungal diseases should be handled by chlorothalonil, if you're applying it according to the label. If the leaves have no spots, then you're probably looking at either normal wear and tear (leaves which are shaded out tend to die off naturally) or some deficiency, whether of water or a nutrient.

If there are no leaf spots (rule that out first!) give them a little balanced fertilizer and see what happens. If nothing changes, check for mites by shaking the leaves over one white and one dark sheet of paper and looking at the paper with a hand lens. If you don't find anything... well, come back and we'll take it from there. :)

--Alison
who thinks the huge amounts of rain many people have had this spring might have had an effect on soil fertility...

Thanks...I put down miracle grow on sat morning and had rains sat and sunday...not all day but some nice rains came in..they are looking much better now...well we are back in the uppper 90s again...and I havent watered since before the weekend...but the ground still seems moist and there not wilting so I will wait until tommorow when we may get some more rain...

Thanks'
Steve