Awakened by "Midnight in Moscow," the Americans began their fourth work day in orbit at 2:00 a.m. Houston time. While the crews had slept, the two ground teams in Houston led by Walt Guy and V. K. Novikov had been watching the pressure levels of both ships and had conferred about the leak between the hatches. They had concluded that after the two hatches were closed and the pressure had been reduced to 260 millimetres the gases trapped between them heated up..
With breakfast behind them and their early morning activities completed, Kubasov and Brand conducted a broadcast session from "your Soviet American TV centre in space," as Kubasov called it. In giving his tour of Soyuz, the Soviet flight engineer pointed out what various instruments were for and televised a picture of Brand in "the kitchen" (the food preparation station) warming up lunch. Stafford reciprocated by giving Leonov and the Soviet viewers a Russian language tour of the command module. Appearing casually simple from the perspective of the home viewer, these broadcasts had required hours of negotiation and planning, just as all other aspects of the flight had.
Kubasov later gave an English language travelogue as the two craft passed over the USSR. At about 8:20, Brand and Kubasov began filming some science demonstrations that could later be used in science classrooms back on earth to demonstrate the effects of zero gravity on various items. During this second transfer, Brand had lunched in Soyuz and Leonov in Apollo. At 10:43, Brand returned to Apollo, and Stafford and Leonov moved into Soyuz. Kubasov then transferred into the command module in this exacting cosmic ballet. With each movement of the crew members, the atmospheric composition of Soyuz had to be checked to make certain that not too much nitrogen had been removed. Once everyone was in place, the hatches between the orbital and docking modules were closed as a further step toward maintaining the proper cabin atmospheres. The highlight of the third transfer - was a space-to-ground press conference. The best lines came when asked how he liked the American food, Leonov diplomatically answered, "I liked the way it was prepared, its freshness."
The crews returned to other items on their flight plan. Slayton, as part of the earth observation experiment (MA-136), took photos of ocean currents off the Yucatan Peninsula and in the Florida straits. Slayton, Brand, and Kubasov assembled the two halves of a medallion commemorating the flight, and then they exchanged tree seeds.
Tom Stafford shook hands with Leonov and Kubasov, bidding them farewell at about 3:49 in the afternoon. He then moved back into the docking module, and the space men closed the hatches for the last time at 4:00. The records indicated that Stafford spent 7 hours, 10 minutes aboard Soyuz, Brand 6:30, and Slayton 1:35. Leonov was on the American side for 5 hours, 43 minutes, while Kubasov spent 4:57 in the command and docking modules.
Although the crew signed off for the evening on schedule at 7:20, they spent an uneasy first few hours. In addition to being very tired from the activities of their fourth day in space, they were jangled awake an hour later by a master alarm that reported a reduction in docking module oxygen pressure. This problem was no real hazard, and it was quickly solved by an increased flow of oxygen into the DM, but it kept the crew from getting all the sleep for which they had been scheduled. When wake-up time came at 3:13 on the morning of the 19th, the crew failed to hear the musical strains of "Tenderness" as sung by the Soviet female artist Maya Kristalinskaya, with which the ground team had hoped to gently waken them. But 15 minutes later, they were awake and ready to begin their fifth day. Next door, beyond hatches three and four, Leonov and Kubasov were getting prepared, too.