evidence: The relation between DPT and SIDS was examined by a previous Institute of Medicine committee in its investigation of the adverse effects of pertussis vaccine (Institute of Medicine, 1991). That committee concluded that the evidence favors rejection of a causal relation between DPT and SIDS. ''Studies showing a temporal relation between these events are consistent with the expected occurrence of SIDS over the age range in which DPT immunization typically occurs'' (Institute of Medicine, 1991, p. 141). Since both diphtheria and tetanus toxoids are components of DPT, it is likely that these toxoids are not causally associated with SIDS, although it is theoretically possible that pertussis vaccine could protect children from an effect of DT immunization on SIDS. Only one study (Pollock et al., 1984) compared the incidence of SIDS in cohorts of children who were immunized with DPT (13,917 doses) and DT (10,601 doses). Seven cases of SIDS occurred within 6 weeks of immunization, three (2.2 cases per 100,000 doses) in the DPT group and four (3.8 cases per 100,000 doses) in the DT group. [...] The evidence favors rejection of a causal relation between DPT and SIDS (Institute of Medicine, 1991). Pollock et al. (1984) presented data suggesting that the relative risk of SIDS after DPT versus that after DT is not significantly different from 1. In the committee's judgment the evidence favors rejection of a causal relation between DT and SIDS.