To eat in McDonalds is not permissible, whether it may be fries, fillet-o-fish or anything else. The reason for this is, that the oil is cleaned out every night from all the sections in one place. There is a very high speculation of close contamination. We do not now for certain what ingredients are being put in their sauces, buns e.t.c. We, as Muslims, should abstain from such places especially when our life doesn't depend on eating frm such places. One must take precautionary measures whilst eating, hence, he doesn't take in any haraam extracts of food into his body.
Answered by Mufti Yaseen Shaikh - Answer Approved by Shaikhul Hadeeth Mufti Farooq (28/1/04)