Natural rubber latex is produced by over 2,000 plant species, and its main constituent is poly(cis-1,4-isoprene), a highly unsaturated hydrocarbon. Since 1914 there have been efforts to investigate microbial rubber degradation; however, only recently have the first proteins involved in this process been identified and characterized and have the corresponding genes been cloned. Analyses of the degradation products of natural and synthetic rubbers isolated from various bacterial cultures indicated without exception that there was oxidative cleavage of the double bond in the polymer backbone. A similar degradation mechanism was postulated for the cleavage of squalene, which is a triterpene intermediate and precursor of steroids and triterpenoids. Aldehyde and/or carbonyl groups were detected in most of the analyzed degradation products isolated from cultures of various rubber-degrading strains. The transient formation of intermediate degradation products with molecular masses of about 104 Da from poly(cis-1,4 isoprene) having a molecular mass of about 106 Da by nearly all rubber-degrading bacteria investigated without detection of other intermediates requires an explanation. Knowledge of rubber degradation at the protein and gene levels and detailed analyses of detectable degradation products should result in a detailed understanding of these obviously new enzymatic reactions.