Line B of the Buenos Aires Underground runs 11.75 kilometres (7.30 mi) from Leandro N. Alem to Juan Manuel de Rosas in Villa Urquiza.

[3][4] In recent years, it has held the title of being the most used line of the Buenos Aires Underground, and its patronage has increased even more after the opening of a section of tunnel between Los Incas station in the neighbourhood of Parque Chas and a shopping centre in Villa Urquiza.

The Japanese units were acquired in the early 1990s, and offer less sitting room than the previous rolling stock, increasing the line's capacity during peak hours.

The open trench approach was used in constructing the Federico Lacroze, Dorrego, Canning (now Malabia), Río de Janeiro (now Ángel Gallardo) and Medrano stations.

Underneath the Rancagua (today Los Andes) park in Chacarita, a workshop and a 10 track garage (with capacity for 110 cars) were built.

Lione B had escalators and turnstiles for the payment of coin-operated service, initially manufactured in the United States, formerly controlled by guards.

On 9 August 9, 2003, two new stations, Tronador - Villa Ortúzar and De los Incas - Parque Chas, were inaugurated, allowing the line to transport more than 300,000 passengers per business day.

[7][8] Initially, the Line B had 56 English Metropolitan Cammell cars, with metal bodywork and two bogies, painted cream and red and with a capacity of 47 seated people.

Each car had 3 double-leaf sliding doors on each side, at platform height, whose opening and closing was controlled by the guard, and had two 105 HP motors.

[9] In 1995, the replacement of the existing fleet began and in 1996 128 second-hand Japanese Tokyo Metro (formerly Eidan Subway) 300/400/500/900 rail cars were purchased that were in excellent condition.

The 5000 series trains, which were in operation in Madrid since 1974, entered service in 2011 to replace some of the Eidan 300/400/500/900 sets that were utilized on line B starting in 1996.