Following criticism from proponents of workstation group support systems about the lack of validity of 'wide-band' group support systems (GSS), a recent article argued that it was inappropriate to attempt to establish the level of experimental validity for such GSS that is demanded by researchers working with 'narrow-band' GSS. It was argued that 'wide-band' and workstation GSS are very different and this means that it is unlikely that the same measures of success would be appropriate. This paper agrees with this view but not with its extension, that the overall validation requirement is different; theoretical validity is a necessary feature of a full evaluation but it is not sufficient by itself -experimental validity must also be sought. This paper argues against the view that since experimental validity cannot be obtained, theoretical validity will suffice. A twin-track research approach involving theoretical and experimental validity is proposed that can unite researchers investigating (almost) all forms of GSS, modelled on the PIMS programme and supported by one of the research frameworks that already exist. 0 1998 Elsevier Science B.V.