1. A total of six hundred and eighty three new chemical entities (NCEs), were marketed in the UK between 1960 and 1987. The number of NCEs introduced annually onto the UK market declined to an average of 20 per year in 1964 and subsequently to only 7 in 1985. 2. Average development times have increased fourfold since 1960 to a peak value of 13 years in 1984. The concomitant decline in effective patent life has resulted in a mean effective patent life of less than 10 years since the mid 1960s and no more than 6 years since the early 1980s, except for the cohort marketed in 1987. 3. The largest contribution to total development time was made by the clinical phase. For NCEs marketed in the mid 1960s it was 3.3 years increasing to a peak of almost 8 years in the early 1980s, and representing on average two-thirds of research and development time. 4. Between 1960 and the early 1970s total development time for central nervous system (CNS) agents, cardiovascular products and anti-infectives had doubled to 9, 8 and 7.3 years respectively. By the 1980s it was averaging 13 years for CNS agents and was 54% and 28% longer than for anti-infectives and cardiovascular compounds respectively.