of one 50-minute episode per week. Lost episodes Like many series of its era, Z-Cars is incomplete in the archives. The period 1962–65 is reasonably well represented; though with big gaps. With the 1967–71 sixth series, when the programme was shown almost every week, material becomes more patchy still. Of the 416 episodes made for this series, only 108 survive: a few episodes each from 1967, 1969, and 1970, but there are no surviving episodes from 1968 or 1971. About 40% of the total 801 episodes are preserved. The original series was one of the last British television dramas to be screened as a live production. With videotaping becoming the norm and telerecording a mature method of preserving broadcasts, the practice of live broadcasting drama productions was rare by the time the programme began in 1962. Going out "live" was a preference of the series' producer David Rose, who felt it helped immediacy and pace and gave it an edge. As a result, episodes were still not being pre-recorded as late as 1965. Most were videotaped for a potential repeat, although the tapes – costed as part of a programme's budget – were normally wiped for re-use. The transfer of a live or videotaped programme to film greatly enhanced its chances of surviving. In the 1980s, the telerecording of the pilot episode "Four of a Kind" was returned to its writer Allan Prior by an engineer. He had taken it home to preserve it because his children had enjoyed the programme and as a result he could not bring himself to destroy it. This and two other early editions were released on a BBC Video in 1993. Two episodes were returned in 2004 after turning up in a private collection; there have been other occasional returns of individual early episodes in more recent years. When Z-Cars returned in 1967 in its 30-minute, twice-weekly format, it was on nearly every week of the year, which may account for its poor survival rate over this period. The 2 × 30-minute format gradually interchanged with the returning 50-minute format, and when the 50-minute format fell into regular use by the series, this coincided with an increase in its survival rate. All episodes from the 1975–1978 period are preserved in the archives. BBC Archive Treasure Hunt was a drive to seek out missing episodes and is still open to information regarding missing editions of