Launch from the Baikonur Cosmodrome; landing 56 km east of Arkalyk.

The crew was originally the backup crew for Soyuz 18A crew, but the launch of this mission had failed. Following a one day solo flight Soyuz 18 docked with Salyut 4 on May 25, 1975. The cosmonauts became the second crew of spacestation Salyut 4. They stayed 62 days onboard. For that reason the focus of the mission research into long-term stays in space, with the crew performing various biomedical experiments (including intensive physically exercise) and growing plants in orbit. They also made solar observations and took photos of the Earths surface. A spectrometer was repaired, a gas analyzer was replaced, and a pumping condenser in the water regeneration system was switched with a hand pump.

On May 29, 1975 and May 30, 1975, biological and medical experiments were performed and the Oasis garden was started. Studies of the stars, planets, Earth and its atmosphere were started on June 02, 1975 and June 03, 1975. Some 2,000 photographs of the Earth and 600 of the sun were reported taken.

More medical experiments were performed in June 1975, and attempts were made to grow plants, including onions. Experiments were carried out on insects, and experiments on varying the work schedule were carried out.

On July 03, 1975, it was announced that the mission would last beyond the upcoming Apollo-Soyuz Test Project (ASTP). To avoid any conflict of resources, the Soyuz 18 crew was controlled from the old Crimean Control Center, while the ASTP Soyuz 19 mission would be controlled from the Kaliningrad Control Center. The Crimean center had not been used since the Soyuz 12 flight. This was the first time the Soviets had to control two unrelated space missions.

The crew remained aloft aboard the station during the ASTP joint flight.

The Salyut living conditions were starting to degrade by July 1975, with the environmental control system failing, windows fogged over and green mold growing on the station walls. The crew donned exercise suits and increased their exercise period to over two hours a day, and on July 18, 1975 began to prepare the station for unmanned flight.

After the landing the cosmonauts exited the capsule under their own power, but it was two days before Pyotr Klimuk could take a 10-minute walk, and a week before he made a full recovery.