Previous serological analysis of untreated splenocytes and L cell transfectants expressing the wild-derived mouse major histocompatibility complex (MHC) class I molecule, Lw16, demonstrated the presence of two forms of this molecule in the cell lysates, one reactive with both the alpha 2 domain-reactive monoclonal antibody (mAb) 30-5-7 and the alpha 3 domain-reactive mAb 28-14-8 (30-5-7+ 28-14-8+), and the other reactive with only the latter of the two (30-5-7- 28-14-8+). Furthermore, the analysis suggested the presence of both forms on the cell surface. Due to the similarity of Lw16 to the inbred mouse-derived Ld molecule, we tested a panel of Ld-restricted and control peptides for their ability to bind to Lw16 molecules. Here, we report that two Ld-restricted viral peptides, lymphocytic choriomeningitis virus nucleoprotein (LCMV NP) 118-126 and murine cytomegalovirus (MCMV) pp89 168-176, significantly increase the number of Lw16 molecules on the cell surface as measured by the mAb 28-14-8, and the proportion of those molecules that are recognized by the mAb 30-5-7. This was further supported by an increase in mAb 30-5-7-reactive molecules in L.Lw16 cell lysates following treatment with either of these peptides. Examination of the stability of the different forms on the cell surface suggested that the 30-5-7+ Lw16 molecules induced with these peptides were unstable and probably lost their Ld-restricted peptides to generate 30-5-7- 28-14-8+ molecules; these latter molecules were also unstable. In contrast, putative 30-5-7+ and 30-5-7- 28-14-8+ Lw16 molecules on untreated cells were stable. Together, these results suggest that two Ld-restricted, viral peptides can induce assembly of or stabilize 30-5-7+ 28-14-8+ Lw16 molecules, mimicking endogenous self peptides. However, the association of the Ld-restricted peptides with Lw16 is apparently not optimal, since it results in unstable Lw16 molecules.