The effects of stable compounds acting on adenosine receptors, 5'-(N-ethyl)-carboxamidoadenosine (NECA: A2 and A1 adenosine receptor agonist) and 1,3-dipropyl-8-(2-amino-4-chlorophenyl)-xanthine (PACPX: selective A1 adenosine receptor antagonist) were evaluated in vitro on doxorubicin-resistant LoVo (LoVo-R) and doxorubicin-sensitive LoVo (LoVo-S) human metastatic cell lines by using the neutral red test for cell growth. The effect of dipyridamole, an adenosine uptake inhibitor, was also evaluated. The drugs had an inhibitory effect on LoVo cell growth. The association of the drugs with doxorubicin enhanced the inhibition of cell growth, particularly for NECA and PACPX on LoVo-R cells. Morphological observation with scanning electron microscopy indicated cytotoxicity of the tested compounds, alone or in association with doxorubicin both in LoVo-R or LoVo-S cells, supporting the hypothesis of inhibitory effect on tumor cell growth.