I found this on the soteriology 101 site...they quoted MacArthur as saying this, so its not directly from him, but them posting what they say he said. I am not saying they're lying, just clarifying...
==Dr. John MacArthur, in his message covering Romans 2:11-16 (mp3 45-20b), gives a summary of those who did not have the written law and have not heard the gospel:
“Creation, conduct, conscience, contemplation, what they do, how they deal with the good and bad in their own life and how they deal with it in the lives of others indicates that they know the law of God as written in them.
Now, here is the most important thing I’ve said yet. The sum of it is this: If they live up to that much light, and they accept that much light, God will reveal to them the full light of Jesus Christ.
I believe that with all my heart. You see, that’s what it says in Acts 17, “He is not far from us if we would feel after Him.” You see? If they would just take what they have and accept that. John 7:17 – mark it down. “If any man wills to do My Father’s Will, he shall know of the teaching.” If the willing heart is there, he’ll know. ” – John MacArthur
Personally, I think Dr. MacArthur swung and missed here.