Evidence has suggested a role for excess bile acids in the pathogenesis of non-alcoholic steatohepatitis (NASH). Fibroblast growth factor 19 (FGF19), a hormone regulating bile acid metabolism, might have therapeutic potential in treating NASH, but studies have been hindered by its hepatocarcinogenicity. Now, a non-tumorigenic variant of FGF19, NGM282, has been assessed in a placebo-controlled phase II trial in 82 patients with NASH. Patients were randomly assigned to receive 3 mg (n = 27) or 6 mg (n = 28) of NGM282, or placebo (n = 27). After 12 weeks, MRI was used to show that 74–79% of patients in the NGM282 groups achieved at least a 5% reduction in absolute liver fat content from baseline, compared with 7% in the placebo group (P <0.0001 for both comparisons). Both doses of NGM282 were well tolerated.