The 1-year incidence of oral mucosal lesions during cytostatic therapy was investigated in 67 patients [34 men and 33 women (mean age 49 years)] out of 79 original patients, being treated for non-Hodgkin lymphoma or Hodgkin's disease. The incidence of lesions during examinations was 43.4%. Recurrent lesions were observed in 19.4% of cases. Mean leukocyte counts were statistically significantly lower (P < 0.01) during lesion periods than before cytostatic therapy in all lesion groups. Leukocytopenia was found in 85.4% of patients with hairy leukoplakia-like lesions (HLL), and in 81.8% of the patients with angular cheilitis. 5 out of 14 patients with oral ulcers (35.7%) had episodes of septicaemia. Mean thrombocyte counts of patients in various lesion groups were normal (< 140 x 10/1). However, low thrombocyte counts were more statistically significant (P < 0.05), when haemorrhages or HLL were present. Clinical candidiasis was diagnosed in 28.4% of patients during the treatment. However, cultivation revealed that 62.3% of salivary yeast cultures were positive. The study reported here shows a correlation between mucosal ulcers and septicemia, and between leukocytopenia, angular cheilitis and HLL. The disparity between clinically diagnosed candidiasis and the occurrence of salivary yeast counts suggests that antifungal drugs might be of prophylactic value during cytostatic therapy.