Responses to antigens that have been previously recognized as T cell-independent are now known to be dependent on some form of T-cell (or T cell-derived) help. This T-cell dependency, however, can be most easily noted when responses to small resting B cells are examined, since responses of larger, size-separated B cells to TNP-Ficoll require little if any T-cell help. The type of ancillary "help" that is required for the responses to type 1 and type 2 antigens exhibits certain similarities as well as differences. Thus, responses to both of these antigens can be stimulated in the presence of L3T4- or L3T4+ cells as well as in the presence of IL2. However, while the presence of IFN-gamma may be significantly inhibitory for the responses to the type 2 antigen TNP-Ficoll, they do not appear to influence the response to the type 1 antigen TNP-BA. Furthermore, while vigorous elimination of NK cell activity from purified B-cell populations enhances the response to TNP-Ficoll, it has no discernible effect on the response to TNP-BA. These results suggest that determination of type 1 and type 2 antigens may be made not only based on the characteristics of the carrier molecule but also on the nature of ancillary help that needs to be provided for these antigens to stimulate optimal responses. Type 1 antigens have polyclonal B-cell activating properties and stimulate responses which are not influenced by IFN-gamma, type 2 antigens have no polyclonal B-cell activating properties and stimulate responses which can be influenced by IFN-gamma.