Because aspirin and indomethacin, two structurally dissimilar anti-inflammatory agents which reduce prostaglandin synthesis, both alter renal function, we studied the effect on renal function of three new nonsteroidal anti-inflammatory drugs which also reduce prostaglandin synthesis. We have shown that ibuprofen, naproxen, and fenoprofen are able to reduce renal function in patients with systemic lupus erythematosus and that such changes are associated with reduced excretion of urinary prostaglandin E (PGE)-like compounds. The changes may attenuate despite continued drug administration. These findings emphasize that renal function must be assessed with caution in patients taking these and perhaps other drugs which inhibit prostaglandin synthesis. © 1978.