This paper presents recent findings on the impact of temperature and ventilation on call-handling performance and selected sick building syndrome symptoms of call center operators near thermal neutral conditions. The blind intervention study was conducted in two call centers in the Tropics that provide complex call-handling services to their customers. Based on principal component analysis, neurobehavioralrelated symptoms were consistently identified as the cluster of symptoms most affected by the interventions. Operator performance, as indicated by the call talk time, was significantly affected by changes in both temperature and outdoor air supply rate. Increasing outdoor air supply, by approximately two times, led to improved operator talk performance by between 7% to 9% at higher temperatures. Decreasing temperature from a marginally warm thermal sensation to a marginally cool thermal sensation at lower ventilation rate also improved operator talk performance by between 5% and 13%. Moderately strong correlation between principal component for neurobehavioral-related symptoms and talk time performance indicates that increased neurobehavioral-related symptoms of about 16% may cause reduction in talk time performance by 8%.