Disulphide and polysulphide crosslinks in sulphur-cured gum vulcanizates of nitrile butadiene rubber (NBR) could be cleaved by treating with hexane-l-thiol (1M) in piperidine for 72 h under nitrogen at 23 degrees C while polysulphide crosslinks could be cleaved by treating with propane-2-thiol (0.4M) and piperidine (0.4M) in toluene for 2 h. Crosslink cleavage can result in freeing significant amounts of the NBR itself from the network: unless this is accounted for, a misleading value of crosslink density will result. Within practical sulphur and accelerator loading an increase in sulphur:accelerator ratio results in an increase in total crosslink density and the proportion of di-and polysulphide crosslinks. An increase in vulcanization temperature gives rise to networks of lower total crosslink density with a higher proportion of monosulphide crosslinks.