Antigen-specific T helper and T suppressor factors are characterized by their affinity to antigen and by determinants controlled by immunoglobulin heavy chain variable region (Vn) 1 and H-2I loci (for reviews, see 1-3). A generally accepted hypothesis suggests that specific T cell factors may be secreted receptors of T cells. It is interesting, however, that whereas the function of most T cells is H-2 restricted, many antigen-specific T cell factors are not H-2 restricted (4-14). It is not clear, therefore, whether some H-2-restricted T cells produce nonrestricted factors, which thus do not completely represent their receptor, or alternatively, the different factors may respectively represent restricted and nonrestricted T cell sets. Because the difference between regular and associative recognition most likely depends on the nature of the receptor, this problem has important structural and genetic implications. Analysis of the question involves studying H-2 restriction of both the cellular receptor and the helper factor from the same T cell clone. Hybridoma clones secreting H-2-restricted (15) or nonrestricted (11-13) suppressor factors have been described. Much less success was achieved, however, in the construction of helper factor-producing hybridomas, and for neither case is there information that would compare factors and receptors.Recently we have described an approach for the preparation of helper hybridoma cultures (16). One of a number of clones was characterized, and it was shown that this clone, T85-109-45, secretes high titers of carrier, chicken gamma globulin (CGG), specific helper factor. It has also been demonstrated that the T85-109-45 factor contains Ia determinants and also determinants shared with the Ig VH framework