The hypothesis is based upon: a) My observed clustering of Sudden Infant Death Syndrome (SIDS) cases at places with abnormal geomagnetic fields (GMF) and/or electromagnetic fields (EMF); b) recorded GMF with pulsations matching the breathing frequencies of infants; c) the reported immature development of increased dendritic spine density in the brain stem of SIDS cases and; d) the increased dendrite arborization in the brains of rats exposed to magnetic fields (MF). The hypothesis consists of two parts: 1. A disturbed GMF in the residence or surroundings of a pregnant woman may interrupt the normal development of the central organ which controls respiration (brain stem) of the fetus. This is termed the 'Selection Factor'. 2. If such an infant with a functional disturbance of the control organ is then exposed to a GMF or EMF with pulsations similar to his own breathing frequency, but inverted in phase, value, form etc then the vital nerve impulses from the respiration control organ to the breathing organs may be disturbed or blocked with fatal effect. This is termed the 'Trigger Factor'. The elements of the 'Selection Factor' and the 'Trigger Factor' together produce SIDS. A program to test such a supposed 'Trigger Factor' is included.