A single intraperitoneal inoculation of 0.01 ml of virus fluid, 10(3.5) to 10(4.5) TCID(50) HeLa cells/0.1 ml, was made in 12 newborn hamsters. From 28 to 96 days after the virus inoculation, all 12 hamsters developed multiple, multicentric tumors in the peritoneal cavity. Histopathologic observations on these abdominal tumors strongly suggest that the so-called adenovirus-typical undifferentiated neoplasm produced by intraperitoneal inoculation may originate in part from a neuronal precursor cell group destined for the myenteric plexus. A histochemical study has indicated no direct evidence that the intracytoplasmic basophilic corpuscle is comparable to that of the enterochromaffin pigment. A cytologic perusal under electron microscopy has merely suggested that the poorly differentiated tumor cells closely resemble those described in undifferentiated neurogenic tumors. The mechanism of selective susceptibility of certain neuronal precursor cells to adenovirus remains unanswered.