Bos indicus-crossbred calves exposed to natural Babesia bovis infection in wet and dry tropical environments in northern Queensland were tested for antibodies using the indirect haemagglutination (IHA) test. There was evidence of maternal antibodies suggesting endemicity of B. bovis in the 2 environments. Within one year 35.3 to 94.6% of the calves had acquired B. bovis infection. The highest titres and most rapid conversion rates were observed just after the wet season when the tick population was at its peak. Clinical disease was not observed. A third group of Bos indicus-cross cattle of varying ages in a dry tropical environment of north Queensland was examined for antibodies against B. bovis and Anaplasma marginale using the IHA and complement fixation (CF) tests, respectively. B. bovis and A. marginale antibodies were detected on the farm but clinical disease did not occur.