The aim of the study was to determine the prevalence of chalkbrood disease co-occurring with and without nosema disease, in order to develop a potential model for decisions about initiating treatment for Nosema apis infection. In addition, the prevalence of Malpighamoeba mellificae (amoeba disease) in nosema-infected colonies was examined. Forty out of 168 colonies examined were found to be infected with N. apis, but macroscopic clinical signs were detected in only 3 of these colonies. Nosema infection was encountered in 54% of the apiaries. In 3 clinically positive colonies the average number of N. apis spores per bee was calculated to be 1.2 x 10(6). Secondary infections (amoeba and chalkbrood diseases) were found to be common in nosema positive colonies (30% and 62.5% respectively). We explored the possibility of using chalkbrood as a sign of nosema infection using Baye's Theorem. The predictive value of a negative test is high, but not of a positive test.