Porcine somatotropin (pST) treatment of pigs consistently improves daily gain and feed conversion ratio but the daily injections involved can be problematic. The sulfhydryl compound cysteamine hydrochloride (CSH) increases somatotropin secretion in several species, possibly through inhibition of somatostatin secretion. Therefore, it is possible that dietary CSH supplementation may provide a dietary means of increasing pST secretion and improving growth performance in finisher pigs. Eighteen female crossbred (Large white × Landrace) gilts (59.2 kg) were allocated to one of three treatments with the respective factors being a control diet, dietary CSH (0.7 g/kg) and intramuscular pST (5 mg/day) for 5 weeks. After slaughter the whole half carcass was cut into primal cuts which were then dissected to a retail level into lean, fat, bone and rind. Over the first 2 weeks of the study daily gain was increased by both pST (+46%, P < 0.001) and CSH (+12%, P < 0.05) while feed conversion ratio was decreased by pST (–30%, P < 0.001) and CSH (–9.4%, P = 0.08) over this period. Over the entire 5 weeks there was a large and sustained increase in daily gain in pigs treated with pST (+38%, P < 0.001), while dietary CSH tended to cause a more modest increase in daily gain (+7.4%, P = 0.06). As a result, final liveweight (+10.6 and +2.0 kg, respectively) and carcass weight (+5.8 and +1.6 kg, respectively) were increased by pST and CSH. Back fat was decreased by both pST and CSH (–1.7 and 1.0 mm, respectively). Total dissectible tissue was increased by pST (+9.1%, P < 0.001) and CSH (+3.3%, P < 0.05). In pigs treated with pST, the increased tissue was primarily as lean (+11.1%, P < 0.008) and bone (+17.8%, P = 0.017), whereas an accumulation of non significant increases in lean, rind and bone was responsible for the increased dissectible tissue in the carcass of pigs supplemented with CSH. In conclusion, dietary CSH increased daily gain and carcass weight and decreased FCR and P2 backfat, with responses being most pronounced over the first 2 weeks of dietary supplementation and not as great as those caused by exogenous pST treatment.