Current density maps computed with the ipsocentric-distributed gauge ab initio CTOCD-DZ method and subjected to orbital-by-orbital analysis are used to follow the changing roles of sigma and pi electrons along the reaction coordinate for the trimerization of ethyne (2) to form benzene (1). The transition state (TS) is seen to sustain a diatropic-induced ring current that is entirely an induced circulation of the sigma electrons; there is no sign of the benzenoid pi current in the TS. On the downhill portion of the reaction path, the first change in the maps is that the inner part of the delocalized sigma circulation is replaced by a central paratropic sigma current as the new sigma bonds relocalize. Only in the final stage of the reaction path does the typical benzenoid diatropic pi ring current grow in. This sequence of changes from a sigma-dominated to a pi-dominated ring current accompanies the change of character of the highest occupied molecular orbital-lowest unoccupied molecular orbital gap from sigma to pi.