The antifungal activity of oxine and copper oxinate was investigated using standardized methods to compare efficacy, discriminate activity patterns, elucidate mechanisms of action and establish attributes of relevance to field use. Both agents were shown to be active against a broad range of physiologically diverse fungi. Species of Aspergillus, Penicillium, Fusarium, Rhizopus, Candida, Rhodotorula and Saccharomyces were significantly more resistant than Pythium, Phytophthora, Sclerotina and Trametes, the difference being greater for oxine than for copper oxinate and in Sabouraud than in Czapek–Dox media. Copper oxinate was generally more active and more broadly and rapidly fungicidal than oxine. Both are fungicidal at low concentrations against significant plant pathogens and relatively active against important spoilage and mycotoxin producing moulds. The MIC (minimum inhibitory concentration) and MFC (minimum fungicidal concentration) for both agents were dependent on method and medium. Neither agent produced changes in morphology, asexual reproduction or differentiation. Oxine and copper oxinate were resistant to inactivation by organic materials, interacted synergistically in vitro and did not elicit resistance on long term exposure. Differences in activity pattern suggest independent modes of action. Oxine is worthy of revisitation as a useful agricultural fungicide and preservative.