In telecommunications, a pair-gain system is a network amplifier system used to increase the strength of signals on paired wires installed to reach distances up to about five miles (8 km). A pair-gain system includes an exchange unit and a remote pair-gain unit.

A pair gain unit typically carries 544 simultaneous circuits via 16 pairs of copper cables. Fiber-optic gain units are also used. The units allow telecommunications networks to serve clients at a greater distance from a central office, and provide expansion capacity for local loops. Pair-gain units are also used to extend networks of digital subscriber lines.

Common systems and components include AheadCom ´s Xess1080 Digital Pair Gain System, Alltek 's SDSL Pair Gain PG08, Ericsson's PGS4/8/12 Digital Pair Gain System, DS-PCM/P Digital Subscriber Pair Gain Platform, and Lucent's Access Interface Unit Hardened Remote.

Visually, pair-gain units are metal cabinets typically resembling small apartment-sized refrigerators alongside or near roadways that overlie communications rights of ways. Vehicle accidents, vandalism or sabotage can result in loss of service for users connected to a central office through a gain unit. To achieve maximum resiliency, pair-gain units are often set back from roadways and protected from vehicle impacts with pylons or fences.

Reduntant regional telecommunications systems installed throughout the 1990s in the United States and in other technologically developed nations, including cellular telephone systems and network communication through cable television infrastructure, have reduced the likelihood of complete communications isolation in a local area served by a pair-gain system.