Experimental and clinical experience with compounds containing antimony have shown that the trivalent compounds are generally more toxic than the pentavalent ones. APT can cause severe pain and tissue necrosis and is therefore not given by intramuscular or subcutaneous injection. APT has the actions and uses of AST, but it is less soluble and more irritating than the sodium salt which is therefore more suitable for intravenous use. Trivalent antimony compounds are toxic when used topically. Adverse effects are similar for all trivalent compounds, and include nausea, vomiting, weakness and myalgia, abdominal colic, diarrhoea, and skin rashes, including pustular eruptions. Hypersensitivity reactions also occur. Respiratory symptoms include cough, dyspnoea, and chronic lung changes. Cardiotoxicity is the most important and may produce arrhythmias, myocardial depression and damage, Stokes-Adams attacks, heart failure, and cardiac arrest. Hepatic damage and necrosis, as well as blood dyscrasias, may occur. Toxic effects on the kidney may follow chronic use. Continuous treatment with small doses of antimony may give rise to symptoms of subacute poisoning, similar to those of chronic arsenic poisoning, due to accumulation of antimony in the body, especially if trivalent compounds are used, because of their long biological half-lives. Reproductive disorders and chromosome damage have been reported; antimony compounds are, therefore, potentially toxic to reproduction and have mutagenic, and oncogenic potential. Antimony compounds should, therefore, not be used during pregnancy or in the presence of hepatic, renal, or heart disease. Pentavalent antimony preparations especially the organic compounds, together with non-metallic synthetic preparations, such as the diamidines, have now replaced APT for use in leishmaniasis. Because of the toxicity of antimony compounds, investigations have been undertaken to reduce their adverse effects by combining them with chelating agents. These preparations appear to have reduced the toxic effects of antimony without affecting the efficacy of the preparations. Liposome-encapsulated antimony products have, more recently, been shown to be much less toxic because of the reduced dose of the antimony compound required for effective therapy. The historical uses of antimony were based on the belief that the topical and systemic adverse effects, for example, skin eruptions and diarrhoea and vomiting, were signs that the condition being treated was responding by being brought to the surface to relieve congestion at the diseased area. There is no evidence in topical use, but there is evidence that such use can cause severe reactions.(ABSTRACT TRUNCATED AT 400 WORDS)