Objective To compare the efficacy of Evans bacilie Calmette‐Guérin (BCG) and Pasteur BCG in eradicating marker bladder tumours and to compare the toxicity of the two strains. Patients and methods Ninety‐nine patients with multiple recurrent pTa or pT1 bladder tumours were allocated at random to six instillations at weekly intervals of either Evans BCG or Pasteur BCG. All tumours were resected except one marker tumour. At cystoscopy 3 months after randomization all tumours including the marker tumour, if still present, were resected. Results The incidence of adverse events was similar in the two groups but numbers were small and only large differences would have been detected. No statistically significant difference in efficacy regarding the response of the marker tumour or the appearance of other tumours at 3 months was noted in the two groups. There was no evidence of stage progression of the marker tumours. Conclusions In multiple recurrent pTa or pT1 bladder tumours clearing the bladder of all except one marker tumour provides a safe and convenient way of measuring the response to intravesical therapy. No significant difference in efficacy or toxicity was detected between Evans BCG and Pasteur BCG.