The aim of this study was to determine if the level of digoxin-like immunoreactivity in post-mortem sera obtained from infants differs according to the cause of death and if the level is related to age, post-mortem interval, cardiac pathology or adrenal weight. Twelve infants whose deaths were attributed to sudden infant death syndrome (SIDS), and 11 infants who died from other causes, had blood sampled between 3 to 53 hours post-mortem from their right atrial cavity. Digoxin-like immunoreactivity was measured, using a specific and sensitive digoxin radioimmunoassay, and was detected in 7 of the infants who died of SIDS and 7 of those who died from other causes. The highest levels were seen in two patients who died from meningococcal sepsis and haemorrhage, hyperpyrexia and encephalopathy syndrome, respectively. No correlation was detected between the digoxin-like immunoreactivity level, gender, age at death, post-mortem interval or cardiac pathology. Digoxin-like immunoreactivity levels correlated with adrenal weight. It is concluded that digoxin-like immunoreactivity is frequently found in infant sera, but levels are not specific to and are no higher in SIDS infants than infants dying of other conditions.