ML204 was identified as a novel TRPC4 channel inhibitor following a high throughput fluorescent screen of the MLSMR library and SAR analysis of active compounds. ML204 inhibited calcium influx through TRPC4 channels activated by μ-opioid receptor stimulation with an IC50 value of 0.96 μM and exhibited 19-fold selectivity against TRPC6 channels in similar fluorescent assays. ML204 blocked TRPC4 channels in an electrophysiological assay with an IC value of 2.6 μM and was also active in fluorescent and electrophysiological assays in which TRPC4 channels were activated by different mechanisms, indicating direct block of TRPC4 channels. Selectivity for block of TRPC4 channels was examined in fluorescent and electrophysiological experiments against closely related TRPC channels and more distantly related TRPV, TRPA and TRPM channels, and against non-TRP ion channels. ML204 afforded good selectivity (19-fold) against TRPC6 channels and more modest selectivity against TRPC3 and TRPC5 (9-fold) channels. Little or no block of TRPV, TRPA, TRPM or voltage-gated ion channels was observed. ML204 exhibited properties useful for a variety of in vitro investigations.