This study was performed to evaluate the relative efficacy of Maharishi Amrit Kalash ambrosia (MAK-5) and Maharishi Amrit Kalash nectar (MAK-4) on murine (B-16) and human (SK-Mel) melanoma cells in culture. Ethanol extract (EE) of MAK-5 (EE-MAK-5) induced morphological differentiation (enlargement of soma and nuclei and formation of long dendritic processes) and growth inhibition in mouse melanoma cells, whereas EE-MAK-5 inhibited only growth in human melanoma cells. Murine melanoma cells were more sensitive (about 3 times) than human melanoma cells in culture to EE-MAK-5; the aqueous extract (AE) of MAK-5 (AE-MAK-5) was ineffective in both cells. Boiling EE-MAK-5 for 10 minutes or exposing it to light at room temperature for 72 hours did not alter growth-inhibiting potency. Ethanol extract of another herbal agent, MAK-4 (EE-MAK-4), inhibited growth in human melanoma cells but not in mouse melanoma cells. AE-MAK-4 was ineffective for both cells. These results suggest that murine and human melanoma cells respond differently to MAK-5 and MAK-4 and that human melanoma growth-inhibiting agents are present in both EE-MAK-5 and EE-MAK-4.