Abstract: Inhibition of RNA function, and treatment or control of diseases or conditions, e.g. infectious diseases such as viruses and viral infections (including HIV) and microbial infections, by the contacting of the RNA with a compound having a central or core structure comprising three fused rings containing from 12 to 15 ring atoms, the central ring including at least one heteroatom selected from nitrogen, oxygen and sulfur, the atoms of the three-ring core structure being optionally substituted with substituents such as halogens, cyano, and/or various substituted or unsubstituted aliphatic and/or heteroaliphatic moieties, or contacting the RNA with yohimbine, usnic acid or N-{4-[2,5-Dioxo-1-(4-trifluoromethoxy-phenyl)-pyrrolidin-3-yl]-phenyl}-2,2,2-trifluoro-acetamide. Preferred compounds are various phenothiazines, including both known and novel compounds.