Utilizing previously published data in Part I and new statistical approaches, we provide evidence that: (1) compared to control infants, SIDS infants have a greater prevalence of low 5-HT1A or 5-HT2A/C binding; (2) the percentage of nuclei with low 5-HT1A or 5-HT2A/C binding was 2–3 times greater in SIDS infants compared to controls; and (3) 5-HT source nuclei exhibited a higher prevalence of low 5-HT2A/C binding compared to 5-HT1A. This evidence concerns the gene HTR1A and sudden infant death syndrome.