The organic heavy liquids form the "older" generation of heavy liquids. The two organic heavy liquids most used at present to effect mineral separations are bromoform (CHBr₃) or TBE (1,1,2,2-tetrabromoethane; C₂H₂Br₄). Bromoform has a density of 2.87 g/mL and TBE a density of 2.95 g/mL. Of these, bromoform has the lower viscosity (1.8 cP) but is considered more hazardous to work with because it has the higher vapour pressure (5.9 mm Hg at 25^oC). TBE has a higher viscosity (9 cP) and a lower vapour pressure (0.02 mm Hg at 25^oC).

Another organic heavy liquid, used when higher densities are required, is methylene iodide. Methylene iodide has a density of 3.31 g/mL, a vapour pressure of 1.2 mm Hg at 25^oC, and a low viscosity of 2.6 cP.

The disadvantage of the above heavy liquids is that they are highly toxic and require stringent conditions to minimise exposure to workers. The most widely used heavy liquids, bromoform and TBE, for example, are thought to be highly toxic. Both liquids can be absorbed through inhalation and ingestion and with bromoform, through the skin. TBE was found to be quite toxic when given in small, prolonged and repeated doses and so has a Worksafe Australia exposure standard of 1ppm (or 14 mg/m³) for a time-weighted average concentration. TBE is known to cause eye, skin and respiratory irritation and headaches, nausea and kidney and liver damage. TBE is also a suspected carcinogen.

Inhalation of bromoform vapours cause nose and throat irritation. It can also irritate the eyes and cause lachrymation. By analogy with the closely related substance chloroform, it could be suspected to cause liver and kidney damage. Animal tests suggest bromoform may be carcinogenic but as yet no human information is available. The 1991 Worksafe Australia TLV standard for bromoform is set at 0.5 ppm due to bromoform's irritant qualities and reported skin absorption.

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