Comets are believed to retain most of the original content
 of the pristine Solar Nebula. Therefore, their study
 provides a unique way to understand the history of our Solar
 System and its relation to the interstellar medium.

 Only periodic comets with gas production rates of at most a few
 10E28 H2O molecules s-1 could be proposed in the Central Program.
 We may expect the appearance of much brighter "new" comets during
 ISO life time. We propose to observe these unexpected, bright
 comets as targets of opportunity. The primary goals are the same:
 to investigate the dust and gas compositions of these objects, to
 probe the molecular excitation mechanisms and the coma physical
 conditions, to monitor the cometary activity and outgassing
 processes as a function of heliocentric distance, to compare the
 behaviour of different objects. However, performing this study on
 much brighter objects than the relatively faint periodic comets of
 the Central Program will allow us to obtain a higher scientific
 return. We propose:

 1) To observe reference spectra with the LWS and SWS.

 2) To map molecular and dust emission with CAM.

 3) To secure low resolution spectra with PHT at different
 heliocentric distances.