- Ebrose: "I am familiar with Archmaester Pylos' study of rare diseases!"
- Samwell: "Oh, you are?"
- Ebrose: "Yes. And shall I tell you how he died? From greyscale! Procedure is far too dangerous, which is why it's now forbidden..."
- — Sam and Ebrose discuss Pylos' study of rare diseases[src]
Samwell Tarly mentions that he may be able to cure Jorah Mormont's greyscale using Pylos' methods, but is rebuked by Ebrose who says that Pylos died of the same disease and, because of this, Pylos' methods are forbidden to be used again.
In the books
In the A Song of Ice and Fire, Pylos is a common maester, not an Archmaester, and is in service to Stannis Baratheon at Dragonstone. He is still very much alive, and at 25 years old, is unlikely to be considered an "expert" in any particular field. He has been training to succeed Maester Cressen. He is kind, friendly and trustworthy.
Pylos treats Davos while the latter is imprisoned at Dragonstone. He also treats Edric Storm, one of Robert's bastards (in the show he was replaced with Gendry), with leeches; the blood-filled leeches are later used in Melisandre's ritual against the three false kings.
Pylos educates Princess Shireen, her cousin Edric Storm, and Davos's fifth son Devan. He does give any of them a slack: he chides Edric for boasting about his father's victories, by pointing out that Robert also suffered defeats, among them at Ashford.
After Davos is raised to the position of Stannis's Hand of the King, he consults with Pylos, fearing that he is not worthy for that office because he is not highborn, veteran knight or educated. Pylos encourages Davos by pointing out that highborn nobles, great knights and educated men were extremely poor Hands, while a simple blacksmith's son was an excellent Hand. He (in the show - Shireen) teaches Davos to read and write.
During one lesson, Pylos shows Davos a letter, which happens to be the distress message from Castle Black. Davos, unlike the former Hand, understands the importance of the message and persuades Stannis to travel north and assist the Night's Watch.
Pylos is one of the people whom Davos gathers, to help him save Edric Storm from being sacrificed. Davos admires Pylos's courage, because he knew well what would be his punishment for assisting Davos.
Later, Stannis travels to the North, leaving at Dragonstone a small garrison. Pylos also remains in Dragonstone.
In the fourth novel, Loras Tyrell conquers Dragonstone. It is not mentioned what has become of Pylos and the rest of the occupants of the castle - whether they have been killed or captured alive.
There is no mentioning in the novels that Pylos has ever researched the greyscale, or any other disease.