The objectives of this study were to determine whether oral prophylactic agents are superior to placebo or no treatment on the incidence of oral mucositis and oral candidiasis for patients with cancer. A Cochrane systematic review was conducted of randomized trials of oral (and topical) prophylactic agents for mucositis and oral candidiasis, anywhere in the world, among patients with cancer (excluding head and neck) who were receiving chemotherapy. Eleven studies were included in the meta-analysis for mucositis. Of the six prophylactic agents used for mucositis, only one--ice chips--was effective (relative risk 0.57, 95% CI 0.43 to 0.77). Fifteen studies were included in the meta-analysis for oral candidiasis. There is evidence that antifungal agents that are partially or fully absorbed from the gastrointestinal tract prevent oral candidiasis and that the partially absorbed agents may be more effective than the fully absorbed agents. The RR for partially absorbed agents was 0.13 (95% CI 0.06 to 0.27). In conclusion, there is weak and unreliable evidence that ice chips prevent mucositis. There is evidence that prophylactic use of antifungal agents, which are absorbed or partially absorbed from the gastrointestinal tract, reduce the clinical signs of oral candidiasis.