The present invention relates to the use of leukotriene B4 (LTB4), variants and derivatives thereof as a therapeutic agent in the treatment or prophylaxis of viral infections caused by human and animal viruses. The present invention also relates to the use of LTB4, variants and derivatives thereof as an anti-neoplastic agent in the prophylaxis and treatment of cancers induced by tumor viruses and in other neoplastic diseases. The human and animal viruses are DNA viruses, such as parvoviridae, papovaviridae, adenoviridae, herpesviridae, poxviridae and hepadnaviridae; RNA viruses, such as picornaviridae, togaviridae, orthomyxoviridae, paramyxoviridae, coronaviridae, reoviridae, oncornaviridae and filoviridae in general, and Retroviridae such as HIV-1 and HIV-2.