We selected 9681 samples of cocaine seized in 16 Spanish provinces between 1985 and 1993 and studied the variations in purity by weight and province of seizure. Temporal variations in purity were also studied for samples from four provinces and the presence of adulterants for a subset of samples from two provinces. Large variations in purity were observed in all strata resulting from crossing the variables weight, province and year. In some provinces, but not in others, we observed a decline in median purity and increasing variation in purity with decreasing sample weight. These results suggest that the median purity of street cocaine (samples weighing less than 5 g) in Spain increased between 1985 and 1993, ranging between 45% and 65% in most provinces at the end of this period. At the same time, variations in purity declined. At the end of the period lidocaine, which was the most frequent adulterant at the beginning, had almost disappeared from samples from Madrid and Seville, and caffeine was practically the only adulterant detected.