Melanocytic tumors as well as multiple neurofibromas were induced in 35 of 88 
Syrian golden hamsters by a single s.c. administration of 100 mg/kg of 
N-nitroso-N-ethylurea applied 48 h after birth. The lesions were all observed 
proliferating in the dermis and demonstrated melanosomes and premelanosomes. 
High cellularity, nuclear atypia and transplantability of the tumors in outbred 
hamsters suggested a malignant nature. Some of the melanomas were 
morphologically heterogenous and contained Schwann-like cells as minor 
components. In addition, transplantation of the melanomas resulted in increased 
schwannian differentiation even for primary tumors which did not contain any 
Schwann-like cell foci. One of the transplanted melanomas mimicked malignant 
peripheral nervous tumor. Schwannian differentiation was also proved by the fact 
that glial fibrillary acidic protein was positive in 22.2% of the cases. The 
present results suggest that the induced hamster melanomas originate from neural 
crest-derived cells which are able to differentiate into both melanocytes and 
Schwann cells.