OBJECTIVE:Recent findings suggest that laboring in hot occupational environments is related to kidney damage in agricultural workers. We examined hydration status and kidney function in 192 Florida agricultural workers. METHODS:Blood and urine samples were collected over 555 workdays during the summers of 2015 and 2016. Urine-specific gravity (USG), serum creatinine, and other kidney function markers were examined pre- and post-shift on each workday. Multivariable mixed modeling was used to examine the association of risk factors with hydration status and acute kidney injury (AKI). RESULTS:Approximately 53% of workers were dehydrated (USG ≥1.020) pre-shift and 81% post-shift; 33% of participants had AKI on at least one workday. The odds of AKI increased 47% for each 5-degree (°F) increase in heat index. CONCLUSION:A strikingly high prevalence of dehydration and AKI exists in Florida agricultural workers.