A number of temperature-sensitive (ts) mutants and one pyrimidine deoxyribonucleoside kinase-deficient mutant of herpes simplex virus (HSV), have been located on the physical map of the genome by means of marker rescue experiments and by the analysis of the crossover points in intertypic recombinants between HSV types 1 and 2. The physical map is compared to the genetic map and certain anomalies identified. Analysis of infected-cell polypeptides specified by intertypic recombinants has allowed tentative map co-ordinates to be assigned to the structural genes (or genes which cause post-translational modification) for many of the polypeptides. Immediate-early, phosphorylated, glycosylated and structural as well as non-structural polypeptides have been analysed in this way and it can be concluded that there is no restriction of any of these groups of polypeptides to either the long or the short regions of the genome. One of the recombinants, 2853, is at least partially "frozen" in one orientation of the long region. This orientation is also the one which exhibits a minimum number of crossovers in three other recombinants.