During a retrospective analysis of the value of neuron specific enolase (NSE) in patients with small cell lung cancer (SCLC) it became apparent that at progressive disease (PD) NSE rose exponentially with a doubling time (NSE-Td) varying from 10 - 94 days. In this study the influence of the NSE-Td on the survival of 29 SCLC-patients has been investigated. A significant correlation between survival from the start of rise of NSE at PD and NSE-Td was observed. By extrapolating the exponential rise of NSE to the start of treatment a theoretical logarithmic value of NSE, called Yr, could be calculated. When the patients were grouped according to the Yr value greater than -1, between -1 and -4 and less than or equal to -4 a highly significant correlation between the survival from the start of treatment and NSE-Td was found in all 3 groups. These preliminary data suggest that by means of NSE-Td and Yr value the survival of an SCLC-patient from the time of rise of NSE and from the start of treatment may be predicted within certain limits.