This paper presents a logical epidemiologic exploration into possible associations between exposures to radium-226 in drinking water and incidence rates for cancers of the bladder, breast, colon, lung, prostate, and rectum. The most striking finding is the increasing gradient of lung cancer for both males and females associated with increasing levels of radium-226. This trend was very significant (p less than 0.002) for males, but not so for females. A possible reason for reducing significance in females is the relatively low incidence compared to that in males. The same gradient holds for males over three different time periods (1969-1971, 1973-1975, and 1976-1978). An obvious alternative explanation that must be considered is differential smoking patterns. This was investigated and does not appear to be the case. Another explanation may be that radium-226 is a surrogate for radon 222 in some other radionuclide(s).