We investigated the major histocompatibility complex (MHC) class I‐restricted presentation of an epitope of the hepatitis B virus small surface (S) antigen particle to cloned murine cytotoxic T lymphocytes (CTL). Efficient L^d‐restricted presentation of the S_28–39 epitope to CTL is observed in cells of different tissue origin pulsed in vitro, either with the antigenic S_28–39 12‐mer S‐peptide, or with particulate S‐antigen. The kinetics of epitope presentation differ in S‐peptide‐pulsed and in S‐particle‐pulsed cells: while a 15‐min pulse with the antigenic peptide sensitizes targets for class I‐restricted CTL lysis, presentation of S‐particles requires 30–60 min to sensitize cells for CTL lysis. Uptake of antigenic material and active metabolism of the presenting cell are required for processing of S‐particles, but not for sensitizing targets with S‐peptides. Intracellular processing and presentation of S‐particles is blocked in cells treated with chloroquine, NH₄Cl, primaquine, or leupeptin, but not by treatment with cycloheximide or brefeldin A. This processing pathway operates efficiently in peptide‐transporter‐deficient, L^d‐transfected T2 cells, revealing a novel endosomal/lysosomal processing pathway for class I‐restricted presentation of peptides derived from exogenous S‐particles.