Rehva Guide No 6 - Indoor Climate and Productivity in Offices - states as its main purpose to establish quantitative relationships of indoor environmental aspects with performance and sickness absenteeism. The following relationships were established: temperature with performance, ventilation with performance, perceived indoor air quality with performance and ventilation with sickness absenteeism. The purpose of this paper is to establish what in practice are, or probably are, the most effective measures to increase performance and decrease absenteeism, given the total of the presently available evidence. We argue that robust measures, like avoidance of indoor air pollution sources, minimizing external and internal heat load, thermal effective building mass, cellular office layout with shallow plan depth, occupant control of temperature, operable windows and providing for adaptive thermal comfort are more effective in increasing performance and reducing absenteeism than less robust measures like diluting indoor air pollution through increased ventilation, controlling temperature through mechanical cooling and open plan workroom layout combined with deep plan depth..