Background ICM+ software encapsulates 20 years of our experience in brain monitoring gained in multiple neuro-surgical and intensive care centres. It collects data from a variety of bedside monitors and produces on-line time trends of parameters defined using configurable signal processing formulas. The resulting data can be displayed in a variety of ways including time trends, histograms, cross histograms, correlations, etc. For technically minded researchers there is a plug-in mechanism facilitating registration of third party libraries of functions and analysis tools. Methods The latest version of the ICM+ software has been used in 162 severely head injured patients in the Neuro-sciences Critical Care Unit of the Addenbrooke's Cambridge University Hospital. Intracranial pressure (ICP) and invasive arterial blood pressure (ABP) were monitored routinely. Mean values of ICP, ABP, cerebral perfusion pressure (CPP) and various indices describing pressure reactivity (PRx), pressure-volume compensation (RAP) and vascular waveforms of ICP were calculated. Error-bar chart showing reactivity index PRx versus CPP ('Optimal CPP' chart) was calculated continuously. Findings PRx showed a significant relationship with CPP (ANOVA: p95 mmHg). Examining PRx-CPP curves in individual patients revealed that CPPopt not only varied between subjects but tended to fluctuate as the patient's state changed during the stay in the ICU. Calculation window of 6-8 h provided enough data to capture the CPPopt curve. Conclusions ICM+ software proved to be useful both academically and clinically. The complexity of data analysis is hidden inside loadable profiles thus allowing clinically minded investigators to take full advantage of signal processing engine in their research into cerebral blood and fluid dynamics.