Electron microscopy of lentigines was performed to study the pigmentation abnormality in two children with LEOPARD syndrome. Giant melanosomes similar to those seen in café-au-lait spots of neurofibromatosis and nevus spilus were found in a lentigine from one of our cases. Our results show that "spherical granular melanosomes" described in neurofibromatosis, are lysosomal-like structures associated with the development of complex melanin granules. Our study also demonstrates that immature melanosomes are present in some keratinocytes of LEOPARD syndrome. This finding is in contrast to the prevailing concept that only mature melanosomes are transferred to keratinocytes. The occurrence of individual melanosomes of normal size and shape in keratinocytes of skin in whites with LEOPARD syndrome, suggests that neither the size of melanosomes, nor the racial differences are the factors determining the distribution of melanosomes in keratinocytes.