Long-period comets comprise even more primitive material than
 short-period comets. Observations of their composition are diagnostic
 of the environment during their formation. There is a more than 50%
 chance that a bright long-period comet will be observable during the
 time of ISO observations. This comet should be observed by a similar
 program as comet P/Kopff in Guaranteed Time Observations. This
 program includes three observation sequences at three different
 heliocentric distances in order to observe the development of
 cometray activity and of coma composition. For estimation of the
 integration time it is assumed that this comet is as bright as
 comet P/Kopff.