From their 1974 double album Chicago VII. In some ways Chicago VII brings back a feeling of their first three albums where there are a number of instrumentals along with the rock arrangements. The first disk is mostly made of up Jazz favor instrumentals. Mongonucleosis is one of these instrumental pieces and was composed by trombone player, Jimmy Pankow.

The song has a real Latin sound to it. It was also recorded during the period that the group was recording in James William Guercio Caribou Ranch Studio and Brazilian percussionist Laudir de Oliveira was a member of the band.

This version is reportedly from a 1977 concert in Amsterdam.