remain unchanged is the one of the three that is used in English. SHe has been in the hospital for a week with pneumonia, and her status has remained unchanged. I have never heard of these other two: stay unchanged, keep unchanged,

Follow-up to Rena's post: well, "kept unchanged" certainly occurs, e.g. In scientific writing: "we studied the cells' behavior for different concentrations of calcium, keeping all other parameters unchanged (while all other parameters were kept unchanged) or the like. Outside of this context, "keeping all other parameters the same" would be preferable (simpler). Stay unchanged is rare, indeed, but not wrong ... The doctors tried everything they could but his condition stayed unchanged ... hm, I'm itching to say "stayed the same" or "remained unchanged" here, but I don't think the first version would be wrong.

Hi Allan, In my mind, the first two are 100% interchangeable, but "remains unchanged" is far more common (also just google-tested it): inflation remained unchanged (= the same) all throughout the early 80s; that part of the test remains unchanged; if the stock price stays unchanged you will lose all the money you invested into the put option. "keep unchanged" is different in usage, because it is an active verb: you keep something unchanged rather than something stays unchanged. So: "we kept that part of the test unchanged = this part of the test remains unchanged (because of what we did)"; we kept the inflation rate steady for the last 5 years = the inflation rate stayed steady for the last 5 years because of what we did etc. Hope this helps. Best regards, Aurelio